It sure sounds like a firewall problem, but maybe it has to do with your IP address. Forgive me if these are obvious things you've already examined: Are you running DHCP from your router? Does your laptop's subnet mask and gateway match up with the rest of the computers?

Try running this at the cmd prompt:

ipconfig /all

Does the correct DNS server appear?

For good measure, run

ipconfig /renew
ipconfig /registerdns