Signal Fluctuations


We have 2 Powerbooks and 2 iMac G5's in a small office using a Linksys Access point. The 2 Powerbooks have nice strong signals (between 3 and 4 bars) but the iMac's only get 1 or 2 bars and quite often have no signal at all. If I put the Powerbooks near to the iMacs, the laptops will have a good signal but the iMacs are still disastrous.

The iMacs have the interference robustness set on and the Linksys Access Point is as high as we can get it and only about 6 feet from the iMacs.

Any ideas?
Are the iMacs using airport origanal or extreme? If they are using origanal they will not have as great a range as the extereme. Other than that I can't think of anything else.