Have you tried plugging the modem into a different usb port? (usb is not the most reliable way of connecting the modem btw, even tech support are aware of that, but if its your only option..)
If you dont want to buy a router (the best option) you could always install a 2nd network card
IIRC ntl_0002 is the correct firmware, I'm sure it was ntl_0003 that caused problems so it was rolled back.
As for a new modem, well the ntl100/120 had a "dodgy" ethernet port on some of them, which could cause a poor connection and sometimes an ethernet cable "could" get jammed in at a strage angle making the modem useless
Not that I would suggest such a thing of course
Had a report of a cat peeing on 1 once...