Thanks for the detailed reply. I would have responded sooner but I have been out of town since noon on Friday.
We had "cycled" the modem and router a time or two, but not to the extent that the "power cycle" entailed. So, we tried that first, and it didn't help. We then disabled the MAC filter and still did not have any luck. Also, before we re-established the MAC filter, we updated the firmware for both the wireless card, and the router. Still no go.
I have heard that Home Premium might be the culprit. We have multiple instances of Home Premium on our network, and I found that that particular OS limits the number of computers you can put on a network. Have you heard that?
I am thinking of upgrading to Professional and see if that helps. If it doesn't, we'll still have Pro on the computer, which is what I wanted in the first place.