In reply to Babika:
I've done this several times but haven't come back the same way, preferring to descend to the Monte Rosa hut, either via the normal route or via the fixed ropes that lead to the col between Dufour and Nordend. The latter gives you a chance to tick Nordend too. Margherita > Dufour is very short and given good stable weather you'll probably have time to spare to include Nordend...
The 30m rope is fine. As for gear, I always carry a token Rock 7, but hardly ever use it, and never carry any cams. That doesn't of course mean that you couldn't use them... Personally I wouldn't weigh myself down with them. I'd take two or three extra slings, a nut or two, a couple of quickdraws (there'll probably be the odd bits of tat here and there) Yes, take an ice screw each - but only as part of your glacier kit
The ascent to Zumstein is easy snow. The descent on the other side has a couple of awkward steps on rocky shelves. The traverse of the col, as far as I can remember is straightforward with a few rock spikes. I remember the ascent on the Dufour side having a relatively delicate slab that you might want to protect and belay, though I can't remember what I used. Once on the ridge there are a few awkward bits getting around or over the little towers. From memory one of these involves a quite exposed traverse on icy ground on the right side. You'll come to the fixed ropes that go down to the col on the right just before the summit.
