You either have ... faulty Ram, or a mismatch in the BIOS, or a corrupted HD, or a corrupted file url.dll
http://support.microsoft.com/kb/326687/en-us
Try;
1. Click
Start, and click
Run
2. Type
MsConfig and press Enter
3. Click Expand File
4. On the File to restore text box, type
url.dll
5. On the Restore from text box, specify the position of the Windows XP CD
6. On the Save files in text box, browse to "C:\windows\system32"
Note: I assume your system drive is C and your system folder is
windows. ** Yours may be at WINNT **
7. Click
Expand
8. Restart your computer
good luck