If you upgrade your router to 'G' or 'N' speeds, you will still be able to connect to the new router with your old 'B' cards, providing you configured it to allow slower 'B' type connections and not only connections at 'G' or 'N' connections which some people/administrators do. If you do connect with your older 'B' cards, you will not gain any greater speeds inless you upgrade your wireless cards as well but none the less a upgraded router will allow you to have a greater signal strength and connect from farther away. They say generally, a B router will provide a signal for a single room, a G router will provide a signal for your home and an N router will provide a signal for your home and outside like on a patio or deck, etc... keep in mind though, even with an N router your signal strength will depend on the size of the building, how many walls it has to travel through and how much interference the signal has to deal with.
