this is HOW to deal with it after it happens, remember it cos it saved my life twice with an earlier 52xx build. Vista now has its own Boot manager to get the Dual boot screen.
This is VERY easy to repair but should you get the message "BOOTMGR missing press ctrl alt and del to restart" then do the following.
- Boot from your XP/2003 Disc
- Once at the main menu, press R to Repair your installation
- Login to your XP/Server Partition from the Repair Console
- Type FIXBOOT