A related question - I have an Nvidia FX 5200 video card, and I have managed to get
compiz to work off and on, but it usually will die or crash the x server, and that was under
Etch (on an Athlon 1ghz machine).
I've gotten beryl to work on occasion, but not reliably, and it usually fails with "not compatible window
manager" messages.
I've done an upgrade to lenny (last week) but not a dist-upgrade because there are problems (as it attempts to want to remove KDE), and so I have that on hold for now.
In migrating from etch to lenny, there seems to be a different repository for the lenny beryl/compiz packages (I have an Italian site in my sources.list:
deb
ftp://ftp.it.debian.org/debian
testing main contrib non-free
and it doesn't find a new package for compiz (as of a few days ago), and when I last tried compiz --replace,
I get an all-white screen and I have to kill the x-window server and restart X.