1. Find the model number of your router, post it here, we can tell you.
2. 54mbps is the current fastest "standard", all of the others are either using Pre-N specs, or something like rangemax.
3. G is the wireless standard. Wireless B is 11mbps, G is 54mbps, N is the new standard which is around 250mbps, but the final specifications are not yet known, so any hardware supporting 802.11N is actually supporting Pre-N.