NAT (network address translation) between home and Air-stream

I have been wondering for quite some while as to the best method of connecting between two networks running different subnets.
Is it usually a computer with two network cards running a proxy server? Can it be done more simply with say a high power USB wifi card and perhaps a bridge in windows - I've noted you can get a 2W USB card for $30 with postage!
Or Ideally, is it possible to attach one of these new N-type to Ethernet dongles directly into a home network, running on the standard 192.168.2.x (don't know how that would go for security)

thanks a lot,
Harry