well when you go from modem to airport to hub - you are puting a couple hurdles in the connection to the network - you might want to spring for this: http://www.xbox.com/en-US/hardware/xboxwirelessadapter.htm

or this: http://www.linksys.com/products/product.asp?grid=33&scid=36&prid=558

that way you can go from your airport which runs the 11g standard right to the xbox. If you use an encryption code on your airport the code may have to be entered in its 128bit long version on the adapter setup - thats because apple's 128bit encryption of passwords is different than pcs. I would probably just setup access restriction on the airport and leave the encryption off to avoid this. have fun!