Okay a couple of ways of doing it

A) it might just work. Even if they say its not supported, it may just work.
B) It may work if you go into the BIOS and change the SATA and RAID settings to IDE Emulation and OFF (these options may or may not be present in your BIOS)

If neither of these work, it means you need drivers for your disk controller

XP only supports loading the drivers off a floppy by pushing F6. Nearly all lapotops wont have a floppy so this isnt really an option. An alternative would be to find the drivers for your disk controller and slipstream them into your XP cd using a tool called 'nlite'.

P.S if the reason you are ditching vista is speed, just reinstall vista using a retail disk. I have worked on many sony laptops with vista and they are all slow as hell. Sony load them up with so much crap. A clean install of vista is nothing like that.