|I assume you can now boot into XP but not Win7? If that's correct, it's due to the way you went about the installation.|
I'm not sure how you did what you did but the best way to dual boot is to install the older OS 1st, then the newer one. In your case, you should have deleted all partitioning, created at least 2 new partitions, then installed XP. Once XP was up & running, then Win7 should have been installed from within XP. If you installed XP after Win7, you overwrote the Win7 boot files. You should be able to fix the boot loader by using EasyBCD.