I upgraded my 5 year old HP Pavilion Desktop T685 to Windows 7 a few months ago and everything went well, all devices worked fine except the Radeon X600 graphics card. Whilst it worked, Google Earth crashed the device and system if I used it in Direct X mode - and software emulation of Open GL mode was slow and limited.
I lived with it for a while, then decided that I would bite the bullet and researched a replacement graphics card. It seemed that the Radeon HD4350 had good reviews, would install easily, was supported by Windows 7, and was a reasonable price.
It came this morning, 2 days after I ordered it - brilliant standard delivery service. I disconnected the power, opened up the PC and poked around - not being a hardware expert. I found where the monitor connected and figured that would be the on the graphics card. I undid the retaining screw, released the old card from the motherboard, and was pleased to see that the new card was indeed totally compatible physically. I pushed it in, did up the retaining screw, and powered it up. The monitor still worked, Windows 7 came up, discovered the new hardware and installed the driver, requested a reboot, and after that it was up and running as if nothing had changed.
I started up Google Earth in Direct X mode and the performance was outstanding - spinning the globe, zooming in and out with speed that I hadn't ever seen previously. I then played a movie via Windows Media player and it started so fast and played prefectly. I also ran a couple of 3D graphics demos from the Internet - and they all worked faultlessly.
So - in summary - it was simple, and it work fantastically well. A great buy for me.