There's got to be something simple I'm missing here so forgive my simple mindedness but, using this code:
<mt:CommentAuthorLink>
The comment author's name is not linked, a Movable Type logo icon is instead. I don't want to MT logo to appear at all and I want the commenter's name to be linked instead. Help, please.

I recommend constructing the link manually. <mt:CommentAuthorLink> is meant to be a convenience mechanism. If you need it to output something differently, the best course of action is to build you own by-line.