Gsters answer is the way I would do it too.

In Photoshop I normaly just create a folder called ColorMap and one called BumpMap and use Photoshops layers to blend together the look I want having all the colour map layers in the ColorMap Folder and the bump maps in the BumpMap folder (strange that - eh!!).

Once that's done I use Maya s PSD file format and I can then apply the texture to the shader and map each folder to each relevant node using one file and one 2d Placement Tool. Then any ammendments I do, in Photoshop, can be seen almost instantly in Maya. Check out this tute from DT on the use of Photoshops PSD Node and Maya...

https://www.digitaltutors.com/chit_ch...ight=Photoshop
https://www.digitaltutors.com/chit_ch...ight=Photoshop

QT 7 is required to view these.

Also Kurts UV texturing Tutorial on the low poly game character covers the use of Maya and Photoshop.