So I've had this issue for a couple of months now. At first I thought it was my router, so I went out and bought a 500GB Time Capsule...needless to say, the problem still persists. Usually, when I log to my iMac I get two bars on the Airport icon. My internet connection is really slow/almost non-existent. What I end up doing is I open network prefrences, run diagnostics, and go through that whole process to have my internet function properly. I have to do this whenever I log in to the computer. I have 10.5.6 and I installed the latest Airport Extreme update before upgrading to 10.5.6. Somebody please help!