ok, im a local technician and i have come across this problem a few times, try grabbing an xp boot / install disk, or a recovery console

when windows boots up to the blue screen, it should have install or repair existing, choose repair (r) and a console much like command prompt should appear, when it does it may ask you for the administrator password, it is usually blank, if for some reason it isnt, you may need to download a linux core password restset disk, which i wont get into here, if it is blank it should now have the prompt eg

c:\

try typing

"fixboot"
without the quotes, it should verify, then when it is done, take out the disk and type reboot, i think that is the command, if not just press the key on the front of you computer to restart, all should be fine now, and btw (by the way) xp requires 64 MB of ram, seriously, thats it