Don't ask me why exactly... But I have always had better luck with the schneider drivers. They are supposed to be pretty sweet. I haven't had a successful installation (meaning 3d accelleration) of official ati drivers yet. If you have, good deal. I can't tell you about a performance difference going from ati drivers to schneider drivers (obviously). I can say that the 3.7.6 drivers are much slower than the 3.9.0 drivers. Finally, I don't know why, but schneider-digital.de took the newest drivers off of their site. I'm sorry if it caused you guys any confusion. I would love to send you guys the .gzip of the drivers, but it's 4.3 MB. And hotmail won't let me exceed 1 MB.
Your best bet is to just check the schneider site every so often to see if they repost the drivers. And, if you can get ati's to work... More power to you.