If you boot from the XP CD, one of the options once it detects your existing Windows installation is to do a "Repair" (NOT the Recovery Console earlier in the installation process). A "repair" will reinstall all the original files over the top of whatever is there, and should fix your problem.
If you haven't started customising Windows and installing applications, I suggest reinstalling Windows on a 20483mb partition, and use the rest of the drive for data.