100Mbps is the max bit rate of a normal wired connection (there are also gigabit connections which is 1000Mbps).
54Mbps is the max bit rate of Wireless G (and A but thats older)
Wireless connection is either A, B, or G (there is also "N" but I don't think it is finalized yet)
A and B are older types, anything made in the last couple years will be compatible with wireless G.
When you computer connects to a network it will tell you the max speed at which you are connecting, on a wired connection this is pretty much always 100Mbps because its a wired connection and not susceptible to interference.
Wireless speed depends on your connection quality. If the router is in your house, you will have no interference and the Wireless G bit rate will be 54Mbps.
If you were to go outside and across the street, your signal strength will drop and you will see that the speed will go down as well.
The connection speed is not an indicator of your internet speed, it is your network speed. This is the speed that your own computers will be able to transfer data between eachother. If you were to copy a file from your desktop to your laptop through the network, it will be limited to a max of 54Mbps because the max speed of your wireless connection is 54Mbps. Note this is a theoretical maximum speed, you will be more likely to reach around 36Mbps or maybe 48Mbps in an actual test.