That's curious. I have never had any trouble connecting to the Apple Extreme, whether at home or work.
Which protection protocol are you using? That could be it. I've found that the simplest is to write the machine ID number into the Access Control of the Airport Base Station, and not bother with passwords, etc. If your machine's ID is in the Base Station, then you'll be logged on automatically.
Also check the transmission strength from your base station. I have one covering a very large apartment, with a number of brick walls in the path of the signal, still no trouble with the Airport Extreme Base Station. I can actually log on to my WiFi with my iPod Touch when I'm at the corner newsagent's stand!
And uncheck Interference Robustness if that's been activated.