you're never going to get an answer from these guys. they have "firewall" confused with "port blocker" and don't even seem to know what an actual firewall is.

nevertheless you should be able to connect marginally, though your ability to download will be extremely limited. (AFAIK, kazaa is the only program which works well with firewalls, though it's completely by accident on their part.)

try connecting one of the workstations directly to the adsl router. if this doesn't work, the adsl router itself will have to be reconfigured.

if it does work, then you don't need a separate machine for a firewall - the adsl router may function as a firewall itself. just connect the adsl router directly to the switch.