To tell ya the truth, I had triple boot with XP being one, and I would get the same error as you trying to boot to XP.
I eventually fixed it but I don't remember exactly how. Use EasyBCD to double check that it is setup correctly. You can also use msconfig.exe, boot tab, for information on troubleshooting.
Edit: I believe you have to edit the boot.ini file on XP partition to point correctly. It is currently looking to boot the wrong partition. Yeah! That was the fix for me heh heh.
Check my posts and this thread here: Dual boot 7 and xp