When trying to connect from my iMac (Intel), OS 10.5.3, to my graphite airport I see the base station but cannot connect. If I run iStumbler I see that the signal level is only 35%.
If I run istumbler from my iBook Graphite (OS 10.3.9) I see the signal level is 104% and it connects with no problem. The Imac sees only the one wifi. It's 4 feet away from the Graphite airport. The iBook sees 10 wifi spots. It's 8 feet away from the Graphite airport.
I think the iMac airport is defective but the AppleCare "clerk" says it is an interference problem and offers no help.