Help please

i know this has nothing to do with CF but Dont know were to post but heres my problem on any kind of video/flash game site EX,youtube,minicip,ebaumsworld,megavideo etc they are very choppy the sounds plays normal but the video kinda looks like a a slide show it skips liek 3 or 4 seconds the plays a sec the skips 3 or 4 secs the plays a sec and so on ... even if i let the whole thing finish loading it still does it i have winxp 512mb ram and 1.40Ghz and also i redid my pc 3 days ago and it wored fine before