I have noticed that when I play HD videos, the playback is bit sometimes slow and jerky. Is it possible to optimize the playback some how?

I noticed the problem in xvid-videos(with 960x528 resolution and ac3 audio). I used Kaffeine-player(uses xine) to playback these videos. Or is there some other player that can play HD-material better?

I use Suse 10 distro (and using OSS sound system). My system is: AMD Athlon 64 3000+, 512MB and old Matrox graphics card. I think that the problem isn't that my computer is too slow, because I have a Windows system with AMD 64 2800+, 1024MB and Ati Radeon 9800Pro that can play these xvid videos perfectly.

I would recommend testing whether this is an engine issue, a kaffeine issue, a codec issue, or a system playback issue. Try using mplayer, which uses a different set of all of the above, except your system. If it works fine, narrow it down step by step by switching kaffeine's playback plugin from xine to something else.