Hello Chocalate, welcome to NST.
Robustness aside, I want to say, you did fine by installing W7 after XP, and that's the way it should be...newer OSes after older OSes.
All you got to do now is download
EasyBCD 2.0, run it, add an XP entry, and let it auto-configure, and you'll have your dual-boot.
Cheers.
Jake
P.S. First link in my sig is the FAQs.