LAN Connectivity Problem in Home Wiring

I am completing LAN wiring in my new home. I've used CAT5e cable and connectors. I have a LinkSys cable router connected to a SMC hub (located in a panel in my 'wire closet'). When I connect either my laptop or my wife's eMac to the outlet in her room, less than 30' of cable away from the wire closet, I received the mesages:

\\<computername> is not accessible.

The network path was not found.

And I am unable to access the internet from either the laptop or the eMac via the wall outlet connection. However, both the light on the PC Card dongle (for the laptop's MultiTech card) and the hub are on, indicating a connection. (Of course, when a crossover cable is used, the lights do not come on and there is no transmission.)

But if I string a straight-thru 30' cable down the hallway from the hub to either of these two computers I can ping and access the other computers on the LAN and connect to the internet.

I have tested the wiring using a loopback plugged into the cable connection at the hub end and and a digital multitester at the computer end. All four wire pairs show continuity and exactly the same resistance (4.0 ohms). Wiring polarities were checked and are correct. I also tested for shorts across the wire pairs: there were none.

I've replaced jacks, cables, even bought a new punchdown tool, and spent more than 3 days trying to troubleshoot/fix this problem without success.

BTW, connections in other rooms (e.g., kitchen, workshop) are working just fine!

So, what subtle (or not so subtle) things could cause the problem? Any suggestions and/or explanations are certainly welcomed.

-Tom