UPDATED 22.02.2018
I no longer have an access to ThinkPad T500, so probably it's the last update you'll receive.

Hi!
I'm one of the many owners of Lenovo ThinkPad T500. It's been a great machine since it was released in 2008, but unfortunately, it has been out of official Lenovo support for some time now. The last operating system with full driver support is Windows 7. On this site I'm going to explain how to get the T500 up and running with the latest OS from Microsoft - Windows 10, especially how to install switchable graphics card drivers.

Drawbacks of Windows 10

Windows 10 is the latest version of Microsoft's operating system. Apart from many great features it brought, some are very controversial. One of those "features" is total automatization of the update process. For inexperience home users this is really a great thing, but for non-standard hardware it can really mess things up, because there is no way to cancel installation of a driver. Even worse, users are no longer prompted that an installation even takes place!

How to install switchable graphics driver

Some versions of ThinkPad T500 have a feature called switchable graphics. It allows to switch between discrete ATI graphics card for graphically heavy tasks and integrated Intel chip to conserve battery power. It's a great feature, but sadly there are no official drivers for Windows 8 and up to support it. Here I'm going to explain step-by-step instructions how to make a clean install of Windows 10 and then proper drivers to get it working. It also should work for other ThinkPad models equipped with switchable graphics such as T400 and W500.
I do not take any responsibility for any damages caused by installation of those drivers or doing anything written on this site. Windows 10 is not officially supported by Lenovo on those machines, so keep that in mind. I was writing this guide in February 2016, so all of this applies to Windows 10 version 1511 from November 2015. Because of the way Microsoft is releasing updates for Windows, it may or may not work in the future.

You should download all the software from link below and save in somewhere, preferably on USB drive before installation of Windows 10, because right after that you shouldn't connect to the internet to avoid automatic driver installation.

Here is the list of software to download:

1. Bios update utility
2. Power management driver
3. ThinkPad Switchable Graphics Driver
4. Power Manager
5. AMD Catalyst™ Driver for AMD Radeon™ HD 4000, HD 3000 and HD 2000 Series

Lenovo has removed the drivers from their main support page. In order to download the drivers go to Lenovo's support page for end-of-life products:

https://download.lenovo.com/eol/index.html

Just in case that Lenovo servers would be unavailable I've uploaded the drivers on my google drive folder on the bottom of this page.
If you downloaded the software, let's get to work!

1. Make sure you've got the latest version of BIOS. The latest is 3.23 or 3.25 depending on a machine. To update your BIOS download and run "Bios update utility".
2. Make sure you've got enabled switchable graphics in BIOS. Check it under CONFIG->DISPLAY set Graphics Device to "Switchable Graphics" and OS Detection to "Enabled".
3. Do a clean install of Windows 10. Make sure you have your wireless switch in ON position, but DO NOT CONNECT to any Wi-Fi network and unplug the network cable before installation. Otherwise Windows 10 will automatically start to install drivers and can mess things up! If you forget this it will be the best to format your disk and start over. When Windows 10 is not connected to the internet during installation, you will be able to create an offline account only. Don't worry, it can be switched to online account later on.
4. Install "Power management driver" - n1cku04w.exe
5. Reboot the machine, you will be prompted for that anyway.
6. Install .NET Framework 3.5 using this guide. It's necessary for graphics driver to run properly. Just select a drive letter of your Windows 10 installation media.
7. Install "ThinkPad Switchable Graphics Driver" - 7vd619ww.exe set it to Windows 7 compatibility mode.
8. Install "Power Manager" - n14u405w.exe When it finishes extracting uncheck "Install Power Manager now" and click finish. Then go to C:\DRIVERS\VISTA\PWRMGRV\ and find a file named "SETUP.INI". Open it in notepad then change "AppName=Power Manager" to "AppName=WIN7_Power_Manager". Save it and run "Setup.exe" with compatibility mode set to "Windows 7" to start the installation.
9. Reboot
10. Right click on the "Power Gauge" now located on the taskbar and switch to "High Power" to enable ATI graphics card.
11. Install the latest driver for ATI card - 13-1-legacy_vista_win7_win8_64_dd_ccc.exe
12. Reboot
13. Again, right click on the "Power Gauge" and switch to "High Power".
14. Connect to the internet for the first time :D Windows will automatically install all the remaining drivers and necessary updates. The screen may flicker, because newer display drivers will be installed.
15. Reboot
16. Enjoy Windows 10 on your ThinkPad :)

As far as I know it's the only way to get switchable graphics working properly on Windows 10. I tried many times to install it without Power Manager (like I did on Win 8.1), because I like to keep things simple, but it didn't worked. The Power Gauge on the task bar is just ugly. If anyone knows how to mod it, please let me know in the comments (yes, I tried to replace png graphics in dll file, but the file is signed and the gauge refused to work completely).

How to install Mobile Broadband and GPS drivers

For those who have Ericsson F3507g mobile broadband card installed, just install drivers from links below. As far as I know, other drivers didn't work with Windows 10. I really don't remember where exactly I got those drivers, sorry :( They are probably from Dell, but they just work, so I don't change them. If you made original drivers working with Windows 10, let me know in the comments. But wait, there is more! Ericsson F3507g comes with GPS built-in, so you may also want to install "ThinkVantage GPS". To get it working when you want, just launch ThinkVantage GPS app. It will wake up GPS receiver and start to acquire the signal. Make sure you've got a good sky visibility, or you can even go outside, since it's not very sensitive indoors. When you turn GPS on for the first time, or if you haven't used GPS for long time, leave your laptop outside for 10-20 minutes. It will download an almanac from GPS satellites.
To make GPS work, you need to have a "data-only" SIM card inserted under the battery. It doesn't need to be valid, without a SIM card the whole broadband card doesn't work for some bizarre reason. Windows 10 will use GPS in maps and other programs as soon as it will fix onto satellites, otherwise it will use Wi-Fi triangulation to determine your coarse position.

1. Mobile Broadband Drivers
2. ThinkVantage GPS

What doesn't work

When ThinkPad Power Manager is installed, do not install "Lenovo Battery Gauge" and these fancy Lenovo modern apps from store. Battery Gauge and Lenovo Companion caused bluescreens with indication that it failed due to TP Power Manager. These apps are useless anyway and require you to install "Lenovo System Interface Foundation" to work.

You will also see an unknown device in device manager called "PCI Simple Communications Controller". It's really Intel AMT management engine interface. If you're a regular, non-corporate use you shouldn't be bothered, since it's used in large companies to remotely manage computers. If you want, you can just install drivers from Lenovo's website for your peace of mind ;)

You may see other two unknown devices. They are the Ricoh 4-in-1 card reader. Just install a driver from the support site.

Please let me know about your experiences with switchable graphics on T500. If anything is wrong or missing in my tutorial, please contact me.

Here is the link to my Google Drive:

https://drive.google.com/drive/folders/0B-lx2g0mMBJ8VVpJNDRwXzRhMXM