I have exactly the same problem, but:
>> Everything works perfectly, except XVideo use sometimes crashes X. If it starts fine once,
>> it will always start fine the rest of that X session. If I log out (and X is of course
>> restarted), then possibly the next time I try XVideo it will cause a crash.
If i log out, without restarting X (i mean, without CTRL-ALT-BACKSPACE), and relogging via XDM, it crashes as soon as i launch something using XVideo. (crash = quit the session, and drop me back into XDM). If i login again, it works fine. If i re-log out and re-log in, it crashes, and so on ..
The only way to get rid of that fscking problem is, if i log out, to restart the XServer with CTRL-ALT-BACKSPACE. Then, re-login and launching mplayer or XawTV won't crash.
I forgot, my stuff:
TNT2, Debian 3.0 stable, drivers Nvidia 1.0-3123, kernel 2.4.18, XFree 4.1.0