This driver only works with Red Hat 6.1 (actually with the kernal version that comes with 6.1) but it DOES work! It is completely unsupported (as evidenced by the fact that they haven't ported it to later kernels). I found it on the ESS website (www.esstech.com).
If you do the install as given then it will install the driver for the current boot session. You will have to add a line to one of your system rc files (probably in /etc/initrc.d would be best) to get it to load at boot time.
Once loaded you can use /dev/modem just like a normal modem on a serial port. I used kppp to get a connection up and running and uploaded this file during that first session...