internet access problems

Hello,

I recently installed SBS on a computer, and am using that computer to share an internet connection between about 8 computers (going through a 16 port switch).  Initially, I decided not to join the computers to the domain, and simply created user accounts on the server that mirror those on the workstations.  Everything seemed to be working fine, until all of the computers were being used at the same time.  Randomly (or so it appeared), the server would cut all of the computers off from the internet as well as the shared folders on the server.  I can temporarily fix the problem by disabling and re-enabling the network connection to the local network, but this only allows about 5-10 more minutes of connectivity.  So, is this some sort of security feature in SBS that keeps non-joined computers out of the domain, and thus off of the internet, or is it more likely that there is a problem with the computer or configuration of SBS?

Thanks for any help.