Movable Type has a built in tag called MTEntryAuthorLink that inserts a linked version of an enrty's author name. It uses the login name of the author.

I wanted to easily insert a linked copy of the author's nickname instead, so I created a plugin that copies MTEntryAuthorLink but uses the nickname instead of the login name.

http://kalsey.com/blog/2002/07/nicknamelink_plugin.stm

The code is completely stolen (with modifications) from MTEntryAuthorLink, so it works identically to the existing tag, including the spam_protect attribute.