internet -> adsl modem -> ethernet hub -> several computers (how to configure??)

[Martin Backlund]

Hi guys!

I am new to RealVNC but am totally amazed so far!  Need some help setting up 
realvnc at my parents' house though...

their internet is set up is like this:

Internet connection is via an adsl modem which connects directly to a 1-to-4 
ethernet hub, and from the hub one ethernet cable runs to my mothers 
computer and one to my fathers laptop.

the two computers have as their ip address 192.168.1.4 and 192.168.1.5 and 
connect to default gateway 192.168.1.1 (which is the modem).  If i enter 
192.168.1.1 in internet explorer it takes me to a setup page for the modem.

the ip address as seen from "outside" is 81.243.236.121 for both computers.

my mothers computer runs windows 98 and my dad's computer runs windows xp.  
i could access my own computer from their house when i was there last but 
can't make the connection the other way.

i am new to the network side of things although i'm ok at computers in 
general.  i've been reading about NAT and stuff but i think i need more of a 
ste-by-step walkthrough.

hope somebody can help me

cheers,
martin.