I can't make any guarantees on this, it worked with my radeon mobility 7500 card thou. make sure compiz is installed, install "fusion-icon", run it and there should be a blue box in your notifications area on your panel. right click, i think it is under "Select Window manager" and select compiz. if this worked, then your window manager should restart and your should have compiz working, but if you don't have a title bar(the top bar with the X, min, and max buttons), then it didn't work. if doesn't work, you can try to select window decorator to be metacity under the fusion-icon right-click menu. I am assuming you have the shames repository in your sources.list, if not here is the site to get the information on the repository and the gpg.
http://shame.tuxfamily.org/repo/?cat=11 (Fusion-icon is only in lenny/sid, but I would guess you are using cutting/bleeding edge software from lenny/sid since you are doing 3d modeling)
report back with all findings. make sure you back things up first just incase, and if need be to uninstall the compiz/compiz-fusion software, search "compiz" under synaptic and or go the the "download.tuxfamily.org" section of the origins in synaptic and uninstall the software.
good luck.
