Glad this thread exists. I've had my ATI Allinwonder 9600 for years (under 2000) and never had a problem with JA/JK2 (only problem I ever had with the card was with the "tv" portion which stopped working, and that was before the digital changeover so I didn't use it much, sadly). I also had an old ATI Mobility Radeon with XP that worked fine.
But, I'll be getting a new machine with win7 (and ATI Radeon HD 6490M) in the next couple of weeks, and I'll let you know how it goes!
Of course I'll be using my old JA CD's, rather than dealing with steam.