As Rob says, there should be enough SATA drivers in XP to load the OS.
Another alternative is to build a slipstreamed XP CD with the correct drivers (
http://www.nliteos.com/index.html apparently makes this easy).
Why do you want to reformat the Sata drive? you could just add the IDE drive, copy the data over. Partition Magic would allow you to extend the partition to cover the whole drive if thats a problem.