Easiest way is to plug it back into the original PC. Boot from the XP cd. Press Enter to install XP (this won't overwrite). Then theres an option to repair Install.
This will run through a quick install process preserving settings. You may need your cd key to hand and you will most likely have to windows update again but otherwise its relatively intact.
One thing to note is that although it may have been some random crash that killed it, it can also be an indicator that the hard drive is on the way out so keep an eye on it.