The "old adv forum" search searches subjects heading.
The "Lyrics and Knowledge search" searches on the message bodies but I'm not sure it has been updated lately.
Alan is wrong about the name next to "From" having to come from a member. It works for guests too. The only complication as long as a consistant name is uses, is that if you had posted both as "GUEST, Dazbo" and (member) Dazbo and clicked on a link for "GUEST, Dazbo", your member posts would not be found on that search.