I wouldn't say you're out of luck. I just bought an HP laptop with Vista on it, and HP provide ZERO drivers for XP and state that they do not support XP for this computer.
Yet here I am, albeit a week later, with my new HP computer and XP finally working reasonably well on it. I have a few quicklaunch buttons which don't work quite right but otherwise it's all fine.
My suggestion is to go to the Sony website to find out all the hardware your system has, what brands and models, etc. Then go to the respective "brand" website to find the drivers for the each piece of hardware - they'll likely have suitable drivers. Also, you may find in some cases that the Vista drivers actually work in XP, as my sound card driver did.
Make a start with that, you'll probably get most if not all of your drivers.
What I'll also add is that it took me about a week to get my system running properly on XP, and that there's no one place to go to for all drivers - like a driver "pack". You're probably wishing to hard to expect that, like I was for a while.
