You can always set photoshop (or other graphical apps) in the preferences. Goto Window -> Settings/Preferences and then select Applications (at the bottom) you can then set up maya to open PSD files of "other images",
I like to use tif's I can then paint the UV's in PS apply it to a material that is applied to the model then paint and reload as next said. tif's allow you to use layers, when your working and update nicely.
"No pressure, no diamonds" Thomas Carlyle