Changing channels on Airport Express

[TyWahn]

Is there a way or a need to change channels on an Airport Express? My computer is probably 20 feet from the base station and I am only getting 3 of 4 bars for signal strength.
Also, since hooking up my Airport, my D/L speeds have dropped from 1875/d to 1275-1350/d Anybody have any ideas?
Thanks!!!

(iMac G4 17-inch)

 

[superbovine]

http://docs.info.apple.com/article.html?artnum=166641

 

[ChrisFromCanada]

Also if you have no protection on your wireless network maybe someone is stealing your bandwidth.