Not being an administrator shouldn't make a difference. This is a hardware problem.
First thing to do is simplify your wireless network. Turn off security. Broadcast the SSID. See if you can connect then.
If that's not the issue it's a signal strength or signal-to-noise-ratio issue.
Download MacStumbler:
http://www.macstumbler.com/ It will allow you to analyze the signal strength of the wireless networks nearby, and (if your network card supports it) the signal to noise ratio. You can see it in a nice graph. You get far better granularity than the little "wireless icon" in the top bar, which really is only useful for being pretty.
Then you can walk around with the laptop and figure out where your deadspots are, and where you get signal and where you don't. There could be metal pipes, ducting, electrical wire, concrete etc. in the wall that reflect or obscure the signal.
Check to see what strength you get when you're in the same room.
Check what you get when the AP is in the doorway of the room.
Check if you get good strength when the computer is right next to the wall, and the AP is directly on the other side.
You'll quickly be able to profile where your signal is dropping out.
