network not available?

Hi Guy’s. We have a network at work consisting of 6 systems connected to a 10/100 netgear switch & a netgear ISDN router. The networks using TCP/IP and assigning the address dynamically.
Uptill recently alls been fine, but then we couldn’t browse the network. The internet connection worked fine on all machines.
I eventually fixed the problem by checking the settings one by one on the systems, which ‘re-built’ the database on one machine.
After that everything was ok.
My questions are:- why is this happening & can I prevent this in future, would altering the registry and assigning a ‘Master browser’ prevent this, and finally if I installed netbeui as well would this work as a ‘backup’?
TIA
Glenn