It is common for subscription sites, MUDS etc to blacklist or warn users who create multiple accounts/ connect to services from identical IP addresses. The solution would be, assuming you were on a DHCP - as you are, to disconnect and reconnect. That would at least get one computer on. My old narrowband ISP did not always assign a new IP when I redialed up (Though this is improbable - it's worth checking an ipconfig /a before you start running through the motions)

I encountered a similar problem with a subscription site. The easiest thing for me to do was to connect via a proxy server. CAWS was my weapon of choice - and what's more delicious it is free.

It is unlikely (if possible) that the server is storing hardware information of a 56k dial-up modem :/ I wouldn't like to state my life on that assumption - but I doubt it. I can't even remember how dial-up technology works *titters*.

I presume by mac address you're stating one of you is connected and you share this dial up via two network cards. As this is internal - the addresses will not be seen by the outside server.

Hidden programmes are a possibility. Some installs hide files (usually within your Win directory) or make registry entries which are not uninstalled with their custom uninstallers.

Arghhhhhhhhh - I suggest buying a tux and visiting your local casino.

Or similarly, as above, contact them