No Printing on Network Printer

Have 3 PCs connected as a WORKGROUP on a peer-to-peer network. All 3 run Win 2000 pro. Printer set up dir/connect to one of the PCs. Netwk is connected to a switch, then to a DSL modem, and then out to phone co./Internet. Recently removed Blaster/Welchia worms. Installed Norton 2004 Anti-Virus & ZoneAlarm firewall. Can’t print on 2 pcs netwked to the 3rd pc/printer UNLESS I DISCONNECT FROM THE DSL MODEM (will print fine when not connected). (Also, pc with printer won’t show in Net Neighborhood when DSL connected.) Error msgs: Print subsystems not avail. Can’t browse Netwk. Print server not found. Can you help?