You might want to look into using a graphics tablet then, lowfat. :P
Not quite the same, I know, but if you have enough buttons available then it would be decent I suppose. Not good for gaming but the same goes for a trackpad.
An interesting note here. Apple's Twentieth Anniversary Mac(TAM) came with a trackpad instead of a mouse. It was detachable from the keyboard and the keyboard even had a leather palm rest. That was 1997 though, so no multi-touch. hehe
Select the file then hit command+i (or select Get Info from either the menu bar or contextual menu) and look for the triangle beside "Open with". Hit that triangle and select your preferred app.
Also, there should be a "apply to all" or something button there too so that all files like it are opened with the same app.
btw, I <3 MenuMeters
Gonna boot up my old G4 and have a look around it's HDD for names of good software in a bit here.