Recording from more than one source.

Is there a way to record from the microphone and another source at the same
time. I've tried to choose two sources but it never works. If you select one
source, like the microphone, and then try to select Aux as well, it makes the
first unavailable. It's really frustrating because it was a simple thing to
do with my old windows program and now with Vista it's not. If anyone knows
how to make it work I'd appreciate the help. Thanks.