XP SP2 stops surfing capabilities

I have installed SP2 on 3 different machines and on all 3 of them the same
thing happens:

I can surf the net for about 2-3 minutes - then am unable to surf. I
unistalled SP2 and things work fine. Reinstalled SP2 same problem - also -
when i am able to get to an update page and try to check for updates - it
says that there are problems and to try again later - these machine are for
customers and to be honest it is embarassing as the same things happens to
them when they purchase a machine and take it home.. Iahve done the ipconfig
/realease, etc...

Also and finally I can ping so the problem seems to be just with IE after a
SP2 install