I have Windows XP. I had to update my drivers for my graphics card to get BG2 to work, as it wouldn't run with 3D accelleration.

It ran fine after I got the drivers though. I noticed something though. Running at 800x600 ingame, the screen didn't switch resolutions to make 800x600 fit the screen. I'm running my desktop at 1024x768, and the screen does resize its self for the game, so I'm playing with about 7/8 of the screen. I haven't been able to solve this problem.
IWD ran with no problems.
WinXP is a really good OS, IMHO. System wide crashes are non-existent, and programs crash less. Its
much faster, too. A small problem to consider: alot of hardware is incompatible with XP. At first, my DVD drive, the printer, digital camera, the scanner, and Joystick wouldn't work. Everything was fixed, except the scanner, and joystick. The scanner still has problems, and we had to buy a new joystick, because #@%&* Microsoft wasn't going to make it compatible.
But all that aside, XP is great.

I recommend it.