map overlay

Hi everybody,

How can I create a translucent overlay of a soil map over a black&white
aerial photograph. The photograph is just importet and rectified. ´r.combine´
seems to have capabilities to do some overlay, but with a limited amount
of colors. Is there any other possebility to to this job? It shoud be a single
cover, I can use for export as well.

Thanks in advance,

Rainer