We kind of discussed TIF vs PSD in the thread linked to below. If you start about 3 or 4 posts in, you'll get the info.
http://www.photocamel.com/index.php/topic,3998.0.html
Otherwise, I'd scan to TIFF and do the PS work in a PSD file it it were me...just to know I had something that met two criteria. I convert all my RAWs to TIFFs, and do work in a PSD and save to JPG. Dumb huh?