hey joopson...you'll have to go under the texture menu....set the resolution for the texture (looks like 1024 x 1024 would be ok for your model)...and click create. The default color will be whatever its set to in the color pallette.

To export it to maya, go under the texure menu and just choose export and save as a .tiff or .psd. Before exporting to maya, you should always click on the flip horizontal button (in Zbrush) or it will show up inverted in Maya (you can flip it in Maya on the place 2d node...the v direction, but I always just do it in Zbrush)