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Does the same thing happen everywhere you connect wirelessly or just one location?
I had a similar problem with my very first wireless router in 2007. It worked fine when connected via an Ethernet cable, but MacBook wireless connections rarely lasted more than 10 minutes without dropping. Turning AirPort off and back on would reconnect for a few minutes. That was an inexpensive Trendnet 802.11b/g model TEW432B, and no combination of router and computer settings ever solved the problem.
Using the computer at other locations with different WiFi sources confirmed that the problem was not with my computer. Once I replaced the Trendnet with a different router from another manufacturer in 2008, (a D-Link 802.11 draft-N model DIR-655), I stayed connected all the time. That D-Link is still in use, and still works flawlessly. Since 2008 we've added a Nintendo Wii, an iPad 2, an iPod Touch, a MacBook Pro, and 2 Canon WiFi printers.