In your ICQ go to Preferences -> Connections. Under Server, click on Using Firewall, Not using proxy. Under User, click on Not using proxy, use the following TCP listen port for incoming event. Put from: 20000 to: 20019 for your 1st computer, 20020 to 20039 for your 2nd computer, 20040 to 20059 for your 3rd computer, etc. etc.
now go to your linksys and forward port ranges to each computer.
example:
20000 to 20019 to 192.168.1.101
20020 to 20039 to 192.168.1.102
20040 to 20059 to 192.168.1.103
etc. etc.
reconnect icq.