Second wifi Connection

Hi,

is it possible, on my Macbook Pro, with Mac OS Snow Leopard or Lion, to be connected to 2 (or more) Wireless networks.

The first one with my Airport(for internet access)

The second througn an external wifi card (just for local access).

If it's possible please tell me how because i was trying to fix that for a couple of days, and i found 0 results

Thanks in Advance