Your "main" pc should not have to "swap" networks. Wireless routers have
wired ports also, and the "main" computer is usually a wired connection to
the router (since it is a desktop in most cases and does not move).
You can have 2 network cards on one computer, a wired one and a wireless one.
With Windows XP, if a computer has both a working cable connecting it to the
network, and a working wireless connection, the cable connection will be used by
preference. http://support.microsoft.com/?id=299540