I have looked around the net a bit and can not figure what I do and do 
not need to know.

I am building a  desktop/ firewall for my girlfriend that has cox. As 
her mother hates me I will not have access to the cable modem before I 
drop off the computer, and will not have a ton of time to configure the 
computer before getting something thrown at me. The computer that I am 
giving away will be protecting the rest of the net from the virus ridden 
piece of s* that my girlfriend's mom will not let me fix.All I know 
about the cable modem is that it is not a router and that it has cat-5 
out. I have no experiece with such things so I am hoping that you could 
tell me of the ramifications *or point me to a guide*.

Should I do anything special when I install debian? (should I tell it a 
bs static ip or what?)
Will I need to find drivers?
How much time should I assume that I will need to invest to get firewall 
builder setup?

Thanks for any help possible.