Windows always puts the files that boot the OS onto the first Active partition (shown in Disk management as both System and Active), regardless of where you install the actual OS files (shown in Disk management as Boot, may also be Active). It's the first Active partition that the BIOS uses to start the boot process, so that's where the system files have to go.
Is there some reason you
need to format?
You can just delete all the files on that partition (Except for the boot files in the Root of C: and the Boot folder)?
You'll have to disable the Recycle Bin for drive C, turn off System Restore monitoring of the C: drive, and also take ownership of the
System Volume Information folder (and possibly others) to be able to delete some of the folders.
You can move the boot files to the Vista partition using the Vista DVD or a Win7 DVD to do a Repair.
If you can't get to your Vista disk easily, you can download the
Windows 7 RC, and use it in place of the Vista DVD to do a Startup Repair.
First, in Disk Management, right click the Vista partition on Disk 1 and click
Mark Partition as Active
Power down the system and disconnect the XP Drive. Since the Vista boot manager is on this drive, it will now be "missing", so we can repair it
Connect the Vista drive in it's place so it will be Disk 0. If these are IDE drives you'll have to change jumpers or positions on the IDE Cable. If SATA drives, just move the DATA cable from the XP drive to the Vista drive.
Boot with the Vista/Win7 DVD
Select your Language settings, click
Next
Click
Repair your computer
It will search for Vista installations and display a list, Highlight the Vista entry and click
Next
Click
Startup Repair. This will restore the "missing" bootmgr to the Vista partition.
When it's finished, click
Finish, and the system should boot to Vista.
HTH
Jerry