I agree with the steel bike - save the suspension for summer. The rest really depends on what kind of winter we're talking about here. You mentioned xc skiing, so I take it you have at least some period of permanent snow on the ground and temperatures well below 0C (at least occasionally).
I personally prefer platform pedals for winter riding for a couple of reasons: the clipless cleat is a heat sink; I like to be able to put my foot down quickly; and I like to wear proper winter boots to keep warm. They're also good if you develop a mechanical problem that prevents you from riding. If it's cold enough, a simple flat will do exactly that.
Studded tyres are a must for me. Nokian makes several great models, I use the Hakkapeliitta W106s. These are designed for road use and add relatively little rolling resistance and weight. They're not your best choice for off-road though.
For me XC ski clothes work well. Depending on your route you may want to carry something extra just in case of the abovementioned mechanical problem. By the time you're done scratching your head and monkeying around and decide to start walking the bike, you'll be cold already if you're dressed to just keep warm during the ride.
Electronics: if it's something you need to use during the ride, choose the right kind of batteries and try to keep the gizmo warm. Li-Ion batteries are the best, NiMHs are the worst. I carry my cell phone in a belt clip, so it stays warm throughout the ride. There's no way I can warm up my LED lights, for example, so I either have a couple of sets of NiMHs or alkaline batteries for those. I also have a dynamo setup in my main winter bike. My VDO bike comp display freezes in the cold, but it still logs in the information. I had a wireless comp setup, but battery drain was huge in winter.
My PDA travels in the pannier, I let it sit for half an hour or so after arriving before switching it on. I don't think low temperature during transport is a particular problem for a PDA/laptop anyway. I'd be more worried about the bumpy ride.
--J