Hmm. Is that what he's trying to do?? I don't quite think that is what he means.
Back to what Brenna (BMK) said: MTEntryCommentCount. This tag provides the number of comments on an entry. If it's not working, we need to take a closer look at how you're using it.
If you're only sticking it in an MTArchiveList, it's not going to work - you need an MTEntries container in there (That's why you're getting the error message about MTEntries! Are you sure that MTEntryDate tag is even working?).
CODE
<MTArchiveList>
<a href="<$MTArchiveLink$>"><$MTArchiveTitle$></a><br>
<MTEntries>
<$MTEntryDate format="%B %d ..."$> <MTEntryCommentCount>
</MTEntries>
</MTArchiveList>
although, I'm not really sure how to give you a code sample, since I don't know what you're trying to do with that MTArchiveList tag.