Playing MKV. Files on VLC has a problem (I think!)

I got whole heap of .mkv files with me right here, most of them are good classic movies. Problem is, when i play them back on VLC performance is slugish, and skippy kind of. I don't know why, is there any other better way to play them?. When i convert them using a converter to avi and play them, they works perfectly fine, and that's not all, i don't see any problems in the converted avi even when i play them toshiba standalone in 32' LCD tv. but when i play from .MKV it's kind of skippy, as if i am trying to play them on a very slow computer. i am running on windows 7 with two gigs of ram and amd X2. i am sure that is enough to play .mkv files right?. any suggestions friends?.