Airport Utility cannot see Airport Express

I would like to reply here because I have a very similar problem. First, I'm using a brand new (2 weeks) MacBook with OSX 10.5.2, a new Airport Express (5 days old) with firmware 7.3.1 used as a base station, and Airport Utility 5.3.1. In the 5 days since setting up this network, I have had maybe 20 hours cumulatively of stable network, working fine. The rest of the time, several things happen. Airport scans excessively and may or may not "see" my network name in the list in the menu bar. It also intermittently sees the networks of 4 of my neighbors. It is not the MacBook, because it works fine if I go to a coffee shop or use one neighbor's non-passworded network.

So, I suspected network interference. I appreciate and understand the suggestion to simply change the channel in Airport Utility. The problem with that is that Airport Utility cannot even find the Airport Express. It scans and (almost) never sees it. In the minority of time in which my network does work, I have tried it again and it might recognize it, but when I try to make changes, it goes into an endless cycle of "reading configuration" and stops there, leaving me unable to change the channel (or make any other changes). Posters on other threads have felt this might be related to either the firmware (7.3.1) or the OS.

The oddest point is that Airport Utility "sees" the name of the network but cannot join, and cannot seem to connect to the Express creating the network to effect changes.

Any suggestions? Any additional settings I could tweak (AppleTalk is on, 802.1x login is enabled)? Any need to do a hard reset of the Express? Exchange it for a new device? Anything? Thanks.