One more thing which I found helpful.

When creating a bumpmap by hand in Photoshop -- have a 3 layed project. 1 background layer, 1 guide layer (be it the actual texture, or a UV Unwrap snapshot), then your layer. Have your layer be on top and draw over the guide layer the bumps you need. Then delete the guide layer, merge, and either export, or invert colors (if you want black white, and white black, and all inbetween switched) then export. It uses the same UV unwrap as the rest of your texture, so you may want to get to learn how to texture before you bumpmap...