M$ web site
^Microsoft?

I don't know how big Vista is, but I know its not 15 Gigs.
Try wiping the drive clean and starting over?

After looking up OCZ Vertex SSD... Solid State drive. Interesting, not familiar with this new technology. My first thought is it could be driver related. Like when Installing XP on a SCSI drive, you have to install a special driver before it can read it and continue.

If those don't work...
Not sure if its a labtop or desktop, but if you can, go back to a normal ATA or SATA drive, and use the SSD for something else.