Network Neighborhood loses computers

I am running a network of 7 computers and a print server. Quite frequently the computers will lose sight of each other in network neighborhood. Some computers also lose sight of the print server. All is usually good after a restart but once they have been on awhile I get access denied pop ups and then the other computer will disappear. I have tried running NETBEUI and that has not seemed to help. The main server is Win2K, there are a few XP home, and Win98. Usually the win98 one are having the trouble. They are all using the same workgroup, hence they work sometimes. A couple of the computers even have trouble connecting to the internet after a startup until I start them again. Any help would be greatly appreciated.