Now, if there was some way to work the partitions and what not with XP I would be just fine, I could move the files from the Vista partition, delete it, and expand the XP partition to take its place, only problem is, XP does not have that tool like Vista does 
well you lost me with this post........
I read that you can boot up under windows XP....... but when you do you do not see the partition that holds Vista? Correct?
does it show where the excess disc space is? or is it missing all together?
the reason I posted above to start with, was so you can go to another PC perhaps, regardless if it is WindowsXP(winXPpro preferably...not sure what WinXP home offers ) Vista, or Windows 7... and plug in the SATA HD ( as described above ) that you are having problems with.. you should see both partitions when you do this..... and can copy/back up the Vista Partition's files you want to save....... then perhaps use a Partition Program and recover the mis allocated disc space.....
as Ghastly mentions sort of, I too do not put much faith into nor do I use the OEM disc repair / recovery console or program....
something that might help people who read these threads, is to offer up more info .......like how was the HD originally set up?
did it come preloaded with WinXP OS from a manufacturer?
or did you install the 1st OS on the HD?
did you setup the dual boot option?
there is a few bit of unknowns regarding your problem, that if known, might help people here, help you find a solution....
from my experience, this always works for me when working on problems for others, trying to recover stuff/files.......