external modem wont work with WINNT

I have a machine dual booting win98 and WINNT 4, external modem (3COM US Robotics) works fine in win98 but I cant set it up in WINNT 4, inserted the modem driver disk, it seems to be doing something as it shows a status bar then disappears and then prompts me to insert WINNT 4 disk into drive A: but doesnt give me the option to browse for any other dirves!! any ideas??