Click start and type in CMD to bring up the command prompt.  In the command prompt type PRINT STOP SPOOLING and hit enter.  Now, leave that window up, and go to C:\WINDOWS\SYSTEM32\SPOOL\PRINTERS and delete the document there.  Once you've did that, you must go back to the command prompt and type PRINT START SPOOLING to restart your print service.  Type EXIT or click the X in the top right corner to close command prompt window.  If possible, it may be a good idea to go ahead and reboot your PC.  If these steps do not clear the print job, you will need to re-install your printer.

NOTE: By default, the command prompt will start you at C:\Documents and Settings\User.  To change the path to point back to the C: just type CD \

For more Windows XP Command Lines check out this site http://www.ss64.com/nt/ .