I have my 360 connected to my Airport Express. However, I am using no encryption or access control or any of that stuff. It is just the default settings for the base station other than the name of the network.
I first had access control set up, and had problems with the 360 seeing the network. Then I tried only WPA and still problems. So I decided to go back to default settings.
Don't have any Windows-machines on the network so I am not worried about security.
The 360 connects every time.
As a side note, I bought this cool shareware program that lets me stream my iTunes and iPhoto to the 360 called Connect360. Check it out! For $20 it is awesome.