Well, as someone would surely tell you to do, read http://www.nvnews.net/vbulletin/showthread.php?t=46678
and especially part 3a.
One thing I see is that the primary mode is 1280x1024. I'd think it's a too high resolution. Maybe you should try 720x576? I once had a problem like the one you described and setting a lower resolution helped.
(Note that I'm not an expert, so I could be completely wrong.)