windows xp installs false modem

I have set up an home internet connection sharing with windows XP on the lead, only to find out that the modem type and driver were wrong.
When I querry the modem it tells me that the device is working correctly and has no conflict problems. I still could not connect to the intenet
Why would windows XP ignore the actual modem card installed and pick up a non-existant one and istall it????????

thanks
Ibrahim huseen
MCSE2000