I have two computers connected to my linksys router. An Win7 (wireless) and my XP SP3 (wired). The Win7 never has any problems. About once a day, I lose http connectivity. I can ping sites, but not use HTTP to get html pages. There are no other errors. When it occurs, suddenly, sites are unavailable (the Win7 laptop is always OK). Also, I have four drives connected via a router; three of them (usb drives) are still accessible when this occurs, but my other, a WorldBookEdition mirrored drive, is not. Only rebooting fixes it reliably. Sometimes, powering down the router (or the cable modem) helps but that is rare. Happens with IE8, FireFox, and Chrome.

Try the Networking forum instead: http://social.answers.microsoft.com/Forums/en-US/xpnetwork/threads~Robear Dyer (PA Bear) ~ MS MVP (IE, Mail, Security, Windows & Update Services) since 2002 ~ Disclaimer: MS MVPs neither represent nor work for Microsoft