Are you sure your router is secure and no-one else can access it?
Best to be on safe side, use Mac address authentication, Turn off broadcasting and use WPA encryption at highest level.
Remember these routers will only work at one speed at a time even though they are both B and G complient. If one client accesses the router with a 11Mb/s card, it will drop everyone down to that speed. The more clients join the more that 11Mb/s is shared and your speed will drop.
If you are sure you are secure then I'd manually set the speed of 54Mb/s on both router and PC rather than leaving it at auto detect and see what happens then.