Question : Problem: Overcoming wireless interference

One of my clients is suddenly unable to have wi-fi in his business.  The building in question has a steel roof, but the access point and the computers in question are all inside.

Prior to three weeks ago, Wi-Fi was no problem, using a 3com office connect WL-553
I have also tried a linksys WAP54G

The worst part of this, is that I can set the WAP and a laptop 2 feet apart and can still only see the wireless network intermittently.  Broadcast is turned on, and all hardware is confirmed working.

We're going to try to hunt down the source of the interference, but can anyone recommend a method or equipment to overcome this interference if we can't eliminate it?

Answer : Problem: Overcoming wireless interference

With your access points off - use NetStumbler and see if it picks up any unknown networks. If not - I would start looking at any computers/laptops ect.. that have a wireless card in them. A bad wireless card that is transmitting junk packets can force any other radios into an infinte wait. Your idea of shutting down everything and bringing stuff back up one at a time could also work to find an offending device.
  Offending devices could be cordless phones, microwave ovens (only when in use though), bad wireless cards and any bluetooth devices.
  You could also try some 802.11a(5GHz) equipment but that would require changing all the radios/cards out.
  The only other thing would be to bring in someone with a spectrum analyzer to see what is actually going on - that's big $$ however.