HTTP Fails Once A Day (or more)

I have two computers connected to my linksys (310) router. A Win7
(wireless) and my XP SP3 (wired). The Win7 never has any problems. About
once a day, on the XP computer, I lose http connectivity. I can ping
sites, but not use HTTP to get html pages. There are no other errors.
Ipconfig/all is the same before the failure and after. 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 a MyBookWorldEdition
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.