I'm not sure if Mandriva has NetworkManager, but NetworkManager makes it very simple. Basically what you need to know is the "APN" of your ISP. For example I am with 3 mobile broadband in Ireland and the APN for that is "3ireland".
If you don't have NetworkManager like me, I'd recommend downloading this script :
Which is the script for connecting with 3 broadband in Ireland. You should only have to change the APN to get it to work although the device name may be different for your modem as well.
Hope that helps,