Windows XP Home windows crashing, internet freezing including video playback lagging

Hello, I'm having trouble with my computer (the problems are in the title) its a spare until I can afford a new one but its very important that I get this problem solved as I'm unable to look for a new job without a computer and in turn I'll be stuck with this heap of junk forever! Maybe its just that the RAM is near enough non-existent but I'm not sure if that would affect the performance to such extents. I wouldn't ask for help unless I was at the end of my tether and I've seen how helpful everyone on this site is, so is there any chance anyone could run a tech amateur through getting this PC sorted? If so it would be greatly appreciated!

Danny.

P.S I can follow instructions and I'm not as incompetent as I make out to be.

Try doing an XP repair:
http://www.michaelstevenstech.com/XPrepairinstall.htm