Suse 10.1 supports USB modems. I have tested one USB modem with Suse , it
detected it & also after configuring it I was able to connect to the Net.
Forget RedHat, it's Fedora now, RedHat only concentrates on the Enterprise segment.
First try with Fedora 5 , download the drivers & install them as @Tech_your_future
has suggested. See if it works. Otherwise try with Suse 10.1.