Fit it to a XP computer with SATA Drivers and Backup your data from there.
As things stand Vista needs to format the drive which will result in the loss of data so that it is usable with Vista. Similarly if you want to return the system to XP you need to wipe the HDD with Vista on it as Vista makes it impossible to reinstall XP onto any drive that has been running Vista.
You can wipe the boot drive with something like Boot & Nuke available for download here
http://tinyurl.com/4rfur
Or you can ring M$ Technical Support and ask them how to resolve this issue but if you have an OEM Copy they are quite likely to bill you for the advice. However if you have the Upgrade Version of Vista M$ Technical Support has to offer you an answer.
Or you can ask at the Windows Vista Community a M$ run Web Site here
http://tinyurl.com/yt8adb
Col