Yahoo messenger uses mshtml.dll to render all of the text in chat and IM windows. That's internet explorer, folks. Unless someone has replicated all of the IE hooks in a drop-in replacement for mshtml, I doubt we'll be seeing yahoo messenger on linux any time soon. IIRC you could use MS dll's with WINE if you already owned a copy of windows, but I doubt codeweavers is going to support that usage. There are, however, a number of good linux clients out there for messenger.