what can happen if we don't have a firewall

Hi everyone. We are a small international school with 22 computers on a lan with 7.3, samba, squid and a fast adsl internet connection. We cannot get SuSE firewall2 to let anything happen at all. It blocks everything. Everything works perfectly without the firewall. We have to make a decision soon as to the amount of time spent trying to get the firewall working (thanks to the patience of all on a related thread on this list) and whether we need it or not. What will happen if we don't have it? Thanks, Steve.