Initially I thought this went in the wrong forum when I saw that your distro was mandrake but your subject line clearly says slackware 10.
You are probably aware that slackware uses a different packaging system (.tgz) than mandrake (.rpm)
You would be better off getting the ltmodem source code for slackware and following the directions. Basically it has you run a script that compiles, installs and sets the symbolic link /dev/modem -> to the proper driver. The only dependencies for the ltmodem is to have the slackware development packages and the kernel source package installed (The d/ and k/ series)
LTmodem page
The ltmodem package I would try for Slackware 10
edited for grammer and for dependencies