It's all about hte lowest common denominator.

The speed you actually download from the internet is dictated by the connection between the router and the phone exchange down the road. This is anything between 1 and 16Mbps.

The speed your computer communicates with the router is anything between 10 and 100Mbps for an ethernet cable, and between 11 and 128Mbps for wireless (Wi-Fi).

The maximum speed your computer communicates with the router is dictated by the lowest speed of the two - so if your computer has a 128Mbps wireless card and the router only works at 54Mbps, your computer will only talk to the router at 54Mbps. This connection has almost no bearing on your connection 'speed' to websites, etc, because as you read above, the router's connection to the internet is much slower - so even if you have a 128Mbps wireless card and router, you'll only actually get data from the internet at 8Mbps (for example).

Hope this helps. If not, think of it this way - you have a 600bhp Cossie that can top 180. But you're stuck on a 30mph road.

a 54Mbps wireless card/USB device will be more than adequate.