you think that's confusing
http://en.wikipedia.org/wiki/Network_bridge
the simple answer is yes ..... sort of - by setting up a bridge (which does exactly what it says)
your problem could start with two PCs though
XP/Vista both have the ability to bridge
your networks must be using different ip ranges
first connect both networks (you must have two network adapters)
also ... in real terms running two wireless networks in close proximity isn't a good idea ... so your new lan could do with being a wired setup!!
in network places .... select both adapters .... right click ... select bridge .....
this config is meant to be used by a single PC (server) ... I'm not certain what the outcome would be bridging two seperate machines (you should really buy a hardware bridge)
the alternative is to use the same workgroup name for both LANs ... and physically move the connections.