Hey Jim. Happens to me at least 2 or 3 times a week. I'm 10 feet from my router and have a booster on it. Do a refreash on the network list and nothing shows up. Not even my neighbors. I know the system is working as the laptop in the house is connected when my drops. Only thing I can do is either reboot the router or the computer and then everything is cool again. I have gotten to the point where figuring it out is just driving me nuts. The only thing I can think of is there is some signal around that is crapping me out every once in a while. One thing I did do that helped, was I got a USB card. Its like this little thumb drive size card.
http://www.dlink.com/products/?sec=3&pid=358
This little thing got great reviews everyplace I was able to read one.
It came with a usb extender cable that I sit on top of my computer desk now, and that has gotten me down to maybe 1 connection loss a week. Freaky wireless.