Kryzon, I use Photoshop and an Intuos graphics tablet for all the painting I do. As for reference, I only use a bit to get an idea for some extra things to put in the room and to try and get the different materials right. One very cool method of solving perspective problems is building the room skeleton in Google sketch up first and then printscreening the right angle and importing it into Photoshop, it usually saves me a LOT of time as then I'll already have the perspective done for me.
I think I should do a little tutorial on my room design, maybe that will help?
Thanks for the comments !