choppy playback of mkv h264 files

hey all.. ok I got a new machine and I cant playback h264 mkv files without the video playing back choppy and stuttering... the audio plays fine. I've tried shark007, flv, media player classic home cinema, cccp, win7 codecs, klite and i forgot which other one. and no fixes. Seems to play the best with wmp 12 with the cccp codec pack installed. I have an emachines amd 1.8ghz 2 gb ram geforce 2650se. all other file formats play fine. is it the cpu?? or not enough ram? I'm soooo lost have tried everything I can think of except overclocking my cpu. ANY HELP would be well appericated. Thank

Install only the Shark007 codecs, nothing else.

Open the Settings Application and look at the bottom,
place a check in the box for SUGGESTED settings.

yeah still the same no change

Your system specs are ... not great.
Can you check the resolution of those H264/MKV files? Try to play one no higher than 720p.

Arc, you are probably using the old version of the Handbrake. In the new one (v0.9.4) they have dropped the support for AVI files. :)

By the way, you have just gave the OP a good idea: if he video is too heavy to play on his system (regardless of the codec or player used), he can convert them to a more simple videos (for example using Handbrake), that would be playable.