Getting a New Modem

Howdy folks.
Welp, I currently have a conexant modem, and I'm pissed that I haven't gotten it to work.
I'm looking into getting a US Robotics 56K External Serial modem.
I actually found a rather good and inexpensive one (hope it works).
Is there anything howto's around here about getting an external serial modem working?
I don't want to buy something that will run me into the same situation I'm in.

The current situation I'm in. I can't install anything for my modem, because it requires me to install to /usr which is on the CD and read-only.
Will I have to do it again for a serial modem, of is there an easy way, or automatic work for serial modems?

Thanks.

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