If my math is correct, you should be able to use a switch with 100 Mbps ports for the cameras (or gig ports) and a gig port for the PC. If you use about any switch with gig ports, assuming other ports aren't carrying traffic, any gig switch should carry the load. If you use a switch with 100 Mbps ports and gig uplink port, some inexpensive switches might not be able to carry such a full load.
Several possible candidate swithes with eight 100 Mbps ports and gig uplink (to connect to server) which look able to carry your load include: Cisco Catalyst Express 520-8PC Switch, Cisco Catalyst 2940-8TT, or Cisco Catalyst 2960-8TC-L.
