I know exactly why this isn't working and you should should forget about dual boot, at least for now that is. Sounds like Vista is set to Recognize AHCI where as you need to Load A driver in order for XP to Load correctly.
There is a much easier way for you to do this. Use Virtual PC 2007 or Virtual Box (much easier) What this does is allows you to allocate system resources to a Guest operating system inside Windows Vista, that way you don't have to mess arround with Dual booting.
Don't get me wrong, dual booting has it's advatages, but I think you would have less Head aches using Virtual PC or Virtual Box.
Learn about Virtual PC 2007 herehttp://www.microsoft.com/windows/products/...pc/default.mspx
and Virtual Box Here:http://www.virtualbox.org/
You'll have to load XP by Mounting the Optical Disc, which is explained on both websites, and you can easily set XP to use IDE as it's interface which
will make life easier for you.
Edited by RandomUser, 24 November 2008 - 07:27 PM.