A friend of mine got stuck trying to downgrade his pretty new Sony VAIO VGN-TZ150N from Vista (it sucks!) to XP. While I was able to to find all drivers for him (they're available for free at esupport.sony.com), he couldn't get through the "blue screen of death" when trying to boot from the Windows XP Pro installation CD. Neither did I. Finally, it worked out to be impossible to install the WIndows XP Pro, unless you're using a bundled installation CD that comes with SP2 already.
It took a huge portion of the day, but finally, I got the CD and the installation went fine. Installing all drivers took the rest of the day, but now everything works flawlessly and much faster (Vista sucks!).
Alternatively, you can always order a Windows XP Recovery CD from Sony at https://www.qdirect.net/Sony/VistaDG.aspx (well, not actually always but before the 6/30/2008) and look for a free shipping promotional code at http://www.sony.com/business/downgrade (at the moment of writing this post it's Q93R7). However, a lot of customers report this to take a lot of time, if ever happens.