Unfortunately it is a sony, so the easiest way to get Vista back onto it would be to get some Sony restore discs (only available from Sony or if you talk really really nicely to your local stockists they may have some). In order to do a clean install with a standad vista disc you would need to remove all the partitions off the hard drive and crae new ones, then have a CD key that is not the one on the bottom of the machine as that will only allow you to validate an install from a Sony image.
Sony may well try and charge you for a set of installation disks, sorry, it is the price you pay for an OEM installation.
'99 3.2V6 Auto Limited.
Some day it will be how I want it to be...