Nipper,
Look in the \windows\system\ folder and you will probably find a regedit.com file. Delete it.
If you check the link I posted just 4 rows up, you find this list of files that need to be deleted:
cmd.com
netstat.com
ping.com
regedit.com
taskkill.com
tasklist.com
tracert.com

Make sure you get them all.

Tom