I had to move the boot files off my XP drive onto my Vista drive before I could get it to boot into Vista only.

I copied the following from root of XP to root of Vista:
Folder
-Boot
Files
-boot.ini
-bootmgr
-ntldr

There was a file, BCD, in the boot folder that was in use from windows and would not copy. So I booted to the Vista DVD and copied it using the command prompt option listed in the repair section.

I don't know that all the above files needed to be copied, but definitely the boot folder and bootmgr file needed to be copied.