A suggestion would be to hard-code the Wireless card's MAC address in the router configuration. That way, you can assign it a static IP address from the router. I've found that some wireless routers, particularly D-Link models, work better in that configuration.
Another thing I would do is install the software utility for the wireless card, so that you can "accurately" monitor signal strength (as nelviticus pointed out). If you see the strength periodically dip below 70% in the software utility you installed, then that could also be the source of the problem. It's possible that the Windows configuration tool "thinks" the connection is still alive, but the router is assigning a new IP lease since the conncetion dropped and came back up. That would explain why restarting the connection resolves the issue.
~cdogg
"Insanity: doing the same thing over and over again and expecting different results." - Albert Einstein
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