I don't know the pec of your machine but you definately need more ram to run windows XP.
Post the machines spec and we can all take a look.
If you have upgraded to XP you will need to make sure you have the latest video card drivers installed so check those on manufacturers website.
How did you upgrade to Xp - if you formatted drive and you havean AGP motherboard you may have to install the AGP miniport drivers which you have to do before you install video card drivers. I only know this ( not 'cos I'm a techo wiz) because I formatted my machine and had similar probs - spent 3 days near to setting fire to machine before someone said 'did you load the agp drivers ?' grrrrr
Apart from that post some more details of machine spec & dig out your motherboard manual ...
Hope that helps and hope you get some more posts