1. Try doing a Repair Install from the XP disk.
http://www.microsoft...ips/doug92.mspx
2. If that doesn't work try doing a Clean install.
http://support.microsoft.com/kb/978307
(Follow Method 1)
This might just save you from having to buy a new hard disk. If the order has already gone through, you should be able to return it if the steps above work.
You might be able to access some files on the hard drive. If you know how to use Command Prompt, or DOS, you should be okay. The following Microsoft article should come in handy :
http://support.microsoft.com/kb/314058
I strongly suggest trying to do the above steps before replacing the hard drive.