We have a section of our forum (Threads, 6.5.5) that we use for classifieds...as of late we've had troubles with this section of our site, and would like to eliminate any replies to the threads...ie, a person creates a thread (classified ad) but no one is allowed to reply, thus eliminating the discussion & tire kickers.

Is this doable, or do would I be best served bucking up for a dedicated classifieds software?

I'm not sure about 6.5.5 but in UBB.Threads7 there is a forum permission "Can reply to existing topics".

So, with that can a user/group "write" a thread, but not reply to it?

Here are the forum permissions possible within 6.5.5:

yeh the perms are far more grained in v7; you can setup a group who can make topics but not reply, or just reply, or just respond to polls, anything really...