Soooo, I'd been searching awhile for a prog that would only put a temp in the system tray. I found this site (first link) that reviews the many choices. I chose Weather Pulse (second link). Many features (you'll want to disable some) and very configurable from view>settings. I stopped loading the screen at boot, the transparent temp on the desktop and the weather symbol next to the temp in the tray. Still, it is the best I've found!
http://www.donationcoder.com/Reviews/Archi...Tray/index.html