Repair boot manager

What a mess, did a XP install on my 350 GB drive, then win 7 install on my 1TB drive, everything was working fine could boot to either XP or win 7 at boot screen. Then I decided to setup up 0 raid with 2 TB drives for win 7, that worked fine, but have to change boot drives in bios to work correctly. I hosed my bootmgr file in XP, I had to rename it in win 7 so I could get XP to work. How can I restore the boot manager so I don't have to change boot drives in bios to access each version of windows.

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