Belkin problems

I have a Belking Pre-N F5D8230-4. I'm having the following two problems:

1. My internet speed is half using wireless compared to my desktop that is plugged into the router. Is there something I should adjust for this? My cable connection is 4mb and I get that on the desktop (wired), but only get 2mb with my laptop.

2. I need to know what, if any, settings I should make for my Xbox 360. I have the wireless adapter connected to the Xbox and it works OK I guess. I was wondering if there are ports that should be opened up. I do have the Xbox's IP address in the DMZ, but I read that the DMZ doesn't really work well.