I am going to assume when you restart your MBP, that it boots into Microsoft Windows XP, and you want to boot into OSX. When restarting your MBP, hold do the Option key. Then you will see two hard drive icons, one for OSX, one for XP. Choose OSX, and it will start up.
If you want OSX to be the start up volume, go to System Preferences-Start up Disk. Choose OSX, and then click on the lock icon.
Computer was a gift? Hmm, Sounds like you need to send it in to the cloest Apple store of Authorised service center. Cheers. 🙂 You have a very very odd problem.
Did you install win.XP via bootcamp?? if so as soon as you press the power button press and hold down the OPTION key which is the ALT key for win.users
then sooner later there will be 2 HD icon appear in your screen use your mouse to select which OS you prefer "as we all knew you prefer OSX"and after your OSX start go to sys.preference and choose your start-up this to OSX.then your done.
just remember to press and hold the option key if you wpuld like to switch.
If you read my post above, you will see I told this person the exact same thing. I guess it didn't work, and since the person isn't giving complete or understandable questions, it's hard to figure out what is really wrong.