Had word back from a few people who say they are having trouble removing Vista RC1 from their dual boot systems. So here is an idiots guide and simple way to remove it.
Boot in to Windows XP as normal, place your Vista RC1 DVD in your drive and go to: Start and Run. Type in “
e:\boot\bootsect.exe /nt52 ALL /force” (without quotes, and replacing e: with the drive letter of your Vista DVD).
Once it's finished reboot your PC to make sure XP boot loader is back to normal, then format your vista partition or drive to remove the files

There will also be 2 backup files left over in your Drive C: (or XP partition) these are Boot.BAK & Bootsect.BAK . These can be deleted as normal.
Thats it, done and dusted