My dad has just bought exactly the same gear. He has the router. 1 wireless in a laptop and one inwireless PCI card in a second PC.
I do believe that there is an option within the routers configuration to do with "getting the full" 108mbs. Also make sure that regions etc are set properly.
ALSO...Is there any thick walls/obstructions between the Modem/Router/Card as this can seriously degrade signal strenth, therefore reducing network speed!
Hope this helps, because this is as much knowlodge on the equipment that I have!!