Well I wouldnt jump right to a format I would try an uninstall the network drivers for my network card after you find a new fresh copy of whatever your network card is an give that a shot if that doesnt work there are a few sites that help you fix network issues like this im trying to think of the sites...
http://www.speedguide.net/tcpoptimizer.php I think that is one of them I dont remember for sure but it might help with it. You might have a few network settings that are to low or way to high. Try running one of the tests an looking into it.
Id recommend you start off by going to broadband an under the broadband tools do TCP/IP Analyzer first an see what that recommends you do etc.