If you prefer, you can use EasyBCD software to restore the Vista MBR and hence the multiboot option..
First install
.net 2.0 in your XP, and then download and install easyBCD (
http://neosmart.net/dl.php?id=1 )
Then go to the
Manage bootloader option, and select
reinstall vista bootloader, and then click
write MBR..
Now when you restart, you'll be able to go into vista directly... you won't have XP, but don't panic. Install easyBCD in vista, and then go to
add/remove entries, and make an entry for XP.. Save the changes and you are done.. You can also select the default OS and the timeout details from this software.
Easy BCD is a very small software, about 850kb in size..!!