According to lspci, my card is an "ATI Technologies Inc RV516", a Radeon X1550 actually. I'm currently running Debian Lenny, linux 2.6.24-1-amd64, with Xorg 7.2-5, and a LCD monitor @ 1440x900.
With fglrx version 8.47.1, I get "BadValue" errors and X restarts when trying to use xvideo output in VLC and MPlayer, with and without composite enabled. The same goes for gstreamer-properties when testing video output. Also GDM hangs at logout and it doesn't stops when shutting down the service by hand.
I tried reinstalling, deinstalling, purging, cleaning and reconfiguring fglrx packages, with no luck so far. I should try setting another screen resolution, but for now I went back to 8.45.5 and it's blocky xv... Guess I'll have to wait 'til another version.