I am trying to get my computer online but I can't get my system to recognize my Diamond Supra external usb modem. I just installed mandrake 9.1 and I want to have some fun learning how to use it but I really need to get it online. Can anyone tell me in non technical terms how to make this modem work or can I buy a modem with drivers that will install in this application? Any help would be greatly appreciated.

Probably no need to buy another modem, just google usb modem drivers and the brand and company name. Either you'll find the official drivers for it, or some generic linux ones which enable most of the features at least.
Installing them should make /dev/modem a link to your working modem, and then using Kppp you can set up your ISP account info and use the modem to get online, much like windows.
It is a 56k modem right? You might use a different dialer for cable, but the driver search should be the same
I honestly dont reccommend using the Mandrake Control Centre to set up your connection.