I have the same modem...
let me find the driver and I will give you the link and instructions...
http://linmodems.technion.ac.il/packages/Intel/
The file you want is
Intel536-460-M91.tgz
After you download it, open a terminal window and cd to the directory where you downloaded it to.
tar xvfz Intel536-460-M91.tgz
Then, switch to the directory you created and do the following as root...
make clean
make 536ep
make install
Now run the connection wizard and the modem will be dev/modem
After it is installed, try connecting with the ppp program...on the first attempt it usually says modem does not respond, click cancel and connect again, it should work.
If this does not work, post back and let me know what happens and I will try to reinstall mine and give you instructions.
Oh...and do not worry about the unable to remove thing....mine said that too.