ok, just got finished reading that issue of teamup on-line. It is indeed Magneto vs. Doom, but there's no real actual combat between the two of them. Doom took over the world with some kind of mind control mist, freed Magneto and told Magneto to try to stop him. Magneto used that electro-chemical trick I talked about in the vs. Hulk thread to unbrainwash Beast and then the two of them did a bunch of stuff that culminated in Doom being defeated and forgetting that he ruled the world.
I will say, however, that there were a couple of specific instances in other issues where Magneto and Doom went at it. Both were inconclusive. In one, Magneto tried to manipulate Doom's armor directly, and Doom reversed the polarity, which sent Magneto flying back. But there wasn't any fighting after that. Iron Man has done that to Magneto too, but because Magneto was TRYING to fight Iron Man, he just started shifting frequencies so quickly that it overwhelmed Iron Man and he couldn't compensate fast enough. Magneto took over his armor as a result.
In the other, Doom was time traveling or something and ended up on Asteroid M. They got into it briefly, where Magneto told Doom to "Begone" and sent Doom flying. Doom got mad, activated an anti-magnetic device and hit Magneto. Before Magneto could respond, Doom got teleported again.
So all their fights were basically a series of smacks that never went to a conclusion.