Using Linux on School Network

I am looking into taking a job at a UK Secondary school. Currently the system is fully Windows Based, with a mixture of windows 95/98/NT/2000 clients and NT & 2000 servers. The main problem they have is security and ensuring that only suitable applications can be accesssed i.e. the internet is not always available. Now I've looked at Squid and it seems to provide useful controlling roles, however are there anyother proxies that offer better or similar authentication rules. What Other available software options are ideal for securing or generally running and maintaining a Windows network, but using a SuSE Linux machine. Adam