Depends on the game. Everquest was mostly RAM and secondly video, probably the same for SWG, Everquest 2 was more video than RAM, Vanguard was everything, Guild Wars runs on pretty much anything decently.
I don't think any mass-market MMOGs really use much network bandwidth, other than for downloading updated files. Well, unless you count Second Life, which was continually downloading the world into a cache as you moved around.