How do I connect my mac mini G4 to my wireless network?

I've recently purchased an airport express base station, and connected it to the mac mini through ethernet. Although i'm not getting any good results. I know i'm doing something wrong, I must be. Also, I was told that airport extreme cards aren't compatible with the mac mini, and was recommended to buy an airport express base station to connect my mac mini to the internet wirelessly. Either, i'm doing something wrong or the employee at the apple store gave me incorrect information.