you mean to get it via dhcp?
Every distributions has slighty different way of doing it. I'll assume that you have mandrake. Easiest way is to set up dhcp while installing mandrake at the first place.
If you didn't do it while installing mandrake then check the following.
Your mandrake probably starts to Gnome desktop or KDE-desktop. There's a program called Control center and using it you can change settings.
Hopefully this answered your questions even little.