what was the error message recieved when it failed to renew the IP address ?
if it was something like "An error occurred while renewing interface 'Internet': An operation was attempted on something that is not a socket" then it could still be a winsock issue.
there's more info here
http://onecomputerguy.com/windowsxp_tips.htm#winsock2
when you lose the connection.... are you able to ping any urls or IP address's... or even a loopback address