Another dual boot question

A week or two ago I had a PSU fail. When my computer wouldn't turn on in the morning I did the usual diagnostics; unplug things one at time test with spare components etc... Any way I qucikly figured out the PSU was dead so I ordered a new one and was back up and running. However when I reassembled the computer after unplugging everything (and removing the m/b) I plugged the HDDs back into different SATA ports from which they orginally came. When I came to boot the computer up I got the error message: 'BOOTMGR missing' or it may have been 'NTLDR missing' I can't remember. I fixed this problem by using the 7 startup repair utility. I have no problem booting into Windows 7, but I have lost the option to boot into my XP install on anther disk. I looked in the boot tab under System Configuration and the only OS showing is this Windows 7 install. So my question is this: how can I get the choice of which OS to boot back?

(I should mention that the XP install is on a different disk from the 7 install).

Thanks,

Luves2spooge

UPDATE: It's taken me a few weeks to get around to sorting this problem out because I have had no need to go back to XP. Until today. After posting the OP I figured I could go back into XP by selecting the HDD with XP on as the boot device at POST. This didn't work which prompted me to check the route of the XP partition and as I suspected there was no BOOT.ini. Would writing a new boot.ini simply solve this problem?

Thanks!

First off, if you are using XP so little and may well abandon it altogether at some point, as many here are doing, why not avoid a tricky dual boot and instead just select the XP HDD to boot using your BIOS boot order shortcut key (F10 on my computer - it will be revealed on first BIOS screen, usually something like "Boot Menu"

Select the XP drive in BIOS and see if it boots. If not, run a repair install on XP to recover its bootability. Boot from XP disk, do not choose first "R" but proceed as an install until it discovers installation, then choose Repair Install. Unplug the Win7 drive to make sure there is no interference.

If you do want to proceed with a dual boot menu, then use EasyBCD to add XP by name, type and drive. It will take some surgery to remove it later but we can help when the time comes.