Security Patch Digital signature

While trying to install the RPC security patch to prevent MSblast worm on a W2K DC, I got a “Software package unknown”. It said the Patch was not signed by Microsoft. When I say install anyway it shuts down saying it can not verify the “update.ini” file.
Efforts to install the certificate associated with the patch has got me nowhere.
This is probally easy stuff but I don’t have a clue what to do get it to install. Any help will be appreciated