Part of the problem is Vista, which sucks up a lot of your computer's processing power just to run itself. If you can turn off some of those features that would help. I forget where those are in Vista, but it's basically your 'Theme'.
Another issue is your browser's cache, where it copies content from sites so webpages load faster. You should clear that out on a very regular basis - mine is set up to dump it every time I close the browser. What are you using? Firefox, Chrome, etc?
mornin, oz. i use firefox. i try to run CC Cleaner every so often, that clears out all the temp files i think. but anything i play on youtube is a start and stop festival of frustration.