ViewMesh to the rescue!
This is what I use when I texture - you won't be able to paint directly on the model, but you won't have to load up the game every time you want to see what changes you have made. Viewmesh can load the model in a split second, you can rotate it around, move the camera, etc. I can't live without it
Here is a viewmesh tutorial, and feel free to ask questions if there is any step you don't understand, or if something gives you problems.
A quick way to load a model instead of opening viewmesh, clicking on "Load," browsing to the proper folder, etc., etc., is to open up the command prompt, cd to your viewmesh directory, and load the model file from there. For example:
Then you can just hit the up arrow to load it over and over, if you are making multiple changes.
*edit*
Another very important way to save time and increase productivity is to use Photoshop Actions or GIMP Scripts. Say for example you are working on a 1024x1024 texture that needs to be rotated, scaled down, and exported into a certain format to be used on the final model. You can do this all by hand, or you can use an action, assign it to a keyboard key, and within a second continue about your work. Between using the command prompt and this shortcut, you are saving quite a bit of time without interrupting your workflow.
