Your router claims to support D-Link's "AirPlus Xtreme G® series of wireless networking devices... these 802.11g compatible devices are capable of delivering maximum wireless signal rates of up to 108Mbps when used together." Your adapter claims to support D-Link's "Super G® with MIMO" technology. Are these compatible for the supposed increase in data throughput? Beats me, but my guess would be "maybe".
Also, this increased throughput is very problematic. It reduces with distance, and if there are other "normal" 802.11g networks in the area, maintaining an "Xtreme / Super" G connection will be difficult, since these devices are designed to drop down to standard 802.11g for compatibility reasons.
A rule of thumb on "g" wifi throughput is divide the claimed data rate by 3. So your 54Mbps standard g would have a real-world throughput of 18Mbps, and this is for a good performing setup. With attention to setup, distance, physical barriers, etc., you can get a "g" wifi to perform up into the 20-25Mbps range, but don't count on it.
Applying the same rule of thumb to your 108Mbps system (assuming it is actually operating at 108Mbps), you would expect to see real-world throughput in the 36 - 50Mbps range - assuming it is not constantly dropping down to lower speeds, etc. Some users complain that when these 108 devices drop down, they are actually slower than standard 802.11g devices.