Well, as far as having Mepis and Fedora on separate hard drives, I would just ditch the Fedora.
Hey! Kaonix. Even though I far prefer Fedora to Ubuntu, I sure as heck wouldn't tell someone to just ditch Ubuntu. I might advise them to lose their Windows install though :-)
Anyway, Gtoman, I can't tell you how to configure your internet connection in Ubuntu, but in Fedora the command (typed into a terminal) is:
The fact that you're using multiple hard drives shouldn't affect a thing. My main home computer is a dual boot FC4/FC5 box with FC4 installed on hdd and FC5 on hdc. It works without a hitch. More to the point would be the type of network interface you're using and what the status of your internet connection is as Kaonix asked. Give us some more info and we can probably get you online.