Need some help with Vista Networking -- I Think ????

Sorry, it's hard to describe my problem ... bear with me.

I am running Windows XP Home SP3 and my dad is running Windows Vista Home
Basic SP1. The rest of the configuration is similar for both machines ...
same ISP, both connected directly to broadband cable modem with no routers
or switches or anything. Both are running the exact same version of a third
party software firewall and Windows Firewall is turned off.

In order to do some auto sync filesharing, and to allow me to connect to his
machine and run it remotely when he needs assistance, we both installed
Gbridge software ( www.gbridge.com ).

Everything works fine with one exception. In our firewall software we opened
up certain UDP ports necessary to allow the software to run properly. We are
restricting these open ports to only certain domains. The problem is that on
my machine I can enter domain names such as ...

n1.gbridge.com
n2.gbridge.com
www.gbridge.com
and <host>.<user>.gbridge.net (an alias that gbridge maintains for our
machines when we login)

but on his machine if I enter these domains in the firewall software the
connection will NOT work. On his machine we have to enter the actual IP
numbers for these domains such as ...

209.40.204.87 ( www.gbridge.com)
209.40.204.128 ( n1.gbridge.net )
209.40.204.244 ( n2.gbridge.net ) and
xx.xx.75.108 (my actual IP address)

for the connection to work properly. Of course my IP address is not static,
and although it doesn't change frequently, I would like to resolve this to
prevent issues should my IP address change.

Like I said, same setup ... that is same connection software, same internet
connectivity and ISP, same firewall software ... the only difference is the
OS. I'm guessing there is some sort of DNS service in Windows Vista that
needs to be turned on and running and currently isn't .... or maybe it's
something else entirely ... I really don't know.

Any ideas where I should start looking?

Oh and one other thing, though I am not technically savvy enough to
understand how this works ... the Gbridge software adds a second LOGICAL
ethernet connection to our hardware device list to do it's work ... just in
case that makes a difference.

Thanks for any help!