Well, before you panic, you can repair this.
Boot your system with the Windows XP Install CD, let the system boot into the Setup. Once in the Setup, choose to run the Recovery Console.
You will now be presented with a screen similar to good old DOS.
At the prompt, type the following command: chkdsk C: /r
Replace C: with the letter of your system drive.
This will go into the File System and repair the damage that caused the BSOD.
Once it is complete, reboot your system as normal and it should come back to life.
Note: This FAQ entry also applies to Windows 2000 installations.