If you upgraded then there is no way. You will have to format and install Windows XP. There might be a Windows.old folder that you could possibly restore but that task is more difficult than jsut a quick format.
Really Norcent i have posted things like this several times. If you would look at some of the Dual Boot questions i have also give many, many, many links for this. You screwed yourself. There is no way you can just use the XP Disc to do a fixboot or fixmbr. YOU UPGRADED!!!! Your XP INSTALL IS GONE!!!!
Format start again.
Anyway I upgraded to vista home basic update
XP is gone since you upgraded to Vista. If you just used a Vista DVD and isntall Vista side by side with XP then you would already have a dual boot system.
Ohh yeah the reason why your games are jumpy....YOU ARE ON BASIC WHICH IS NOT MEANT FOR GAMING!!
Basic is just meant to be used on PC's that are only for web and email with some light music. You should have spent more $$ and got Home Premium. Then you wouldnt have this issue. So no matter what you will never be able to game properly on Basic. Hench the name BASIC
. If it was menat to be used as a real OS it would have been Home Premium!