first,, you make the resotre cd for your machine. most new lappy's have a util to make a restore cd.
This cd was normally given to you when you buy. Today they include it on your hd and you make your own from that.
Do not do anything until you have at least two sets of those cd's handy.
Second. Find all the drivers for you machine. You want two sets. one set is the vista and the other set is the XP.
Do not do any thing else until you have both sets.
Then since your lappy is likely SATA you will make a slipstreamed XP install cd. Go find nlite, down load it and it will help you make your XP install disk.
Or find a guru who has the experience and let him ddo it for you.
I just did another vista to XP install. It cost him $125.00 for me to get his machine to run. The secret is to get the F keys and volume control to work.