Each of my two computers have an external serial modem. One uses a Hayes Accura External V.92 Faxmodem and the other uses a Zoom 3048L V.92 Faxmodem. Both work great with Linux. On my newer computer I mostly use Red Hat 9 and on the old computer I mostly use Red Hat 8. I have several versions of Linux on each computer but do not happen to have Mandrake installed at the moment, so I can not describe the exact procedure for Mandrake.
Almost any external serial modem is easy to install under Linux. External USB modems are not always as easy however. No special driver was required when I installed the modems. Below I have attached a link to where I described what little I had to do to make it work under RH8. In that thread, in posts number 4 and 5, I described what I did. Those instructions would be slighly different for other Linux distros. Not all versions of Linux have a command called "neat". If "neat" is not available, then there probably is some other point-and-click type progam on your computer than will walk you through the process step by step. Also notice in my two posts where I said that on some computers one of the two serial ports is useable when the computer already has an internal modem in it. Below is a link to the other that thread:
To connect to your Internet provider you will also need to know the phone number, provider name, login name and password. I was able to find all that from within Widows by clicking on the icon for connecting to my internet provider. The icon was within one of the Windows menus. If you do not want to look for that information in Windows, just call your internet provider and ask them.
After you do that and get connected to the Internet you will eventually want to send and recieve e-mail. If you receive mail from a POP mail account you will need to know the Name of the Pop Mail server. If you use an SMTP server to send mail you will need to know the name of the SMTP server. That information should be entered into your browser somewhere deep within one of the menus. In Mozilla you need to click on the e-mail icon and then look inside one of the pull-down menus within the e-mail Window. You should be able to get that information from within whatever browser you use for Windows or call your Internet provider.
Some versions of Linux such as Slackware require slighly more information that that. I doubt that Mandrake would require anything more. As I mentioned earlier, I do not know the eact procedures for Mandrake. It shoud be easy however. Both Red Hat Linux and Winows 2000 consider my external serial modem to be a Generic modem that does not require a special driver. I mainly had to specify where it is connected and then provided information about how to connect to my Internet provider. As for the question from nemesisza, I belive that almost any exernal serial modem would be a generic modem and not require a special driver. However, many external USB modems are winmodems are are not always as easy to install.