Re: SLR LENS for Antartica 2009!
Reading through the above threads and in particular poindexters blog I think it's a question of what you are happy doing and like using.
My Antarctic shots here are on 35mm film with a set of lenses that between them delivered better quality than current digital slr's. With the quality/weight/equipment issue perhaps less critical than with digital (35mm is lighter and with quality - pixel equivalent - that digital still struggles to match) my priorities were elsewhere.
Stability is critical, I wouldn't carry a tripod every where as it slows you down and limits where you go. A monopod and bean bag would be my preference. The best accessory you have is your legs to get the best place to take your picture. I think a waist camera bag is far better than a backpack (though you should have both).
As for water proof, I never had a problem with a standard rucsac and waist bag with internal drawcords keeping my gear dry. The only problems I ever saw were when people dropped their camera into the sea and that happened when it was out of a bag.
The majority of my pictures on this site were taken with either a 50mm or 100mm fixed lens which was never more than about 5 seconds from readiness.
I also think that the experience of "being there" is important too, you can't get this so well if you are viewing the world through a camera lens. Sometimes I would leave my camera gear behind deliberately.
Of course planning and a tripod will get you some great shots, but not all of them and you will have to carry all the gear around. I'd go for the faster moving and more flexible approach without any lens outside of 28-200mm. I spent a lot of time taking pictures when other people did and I know I got plenty they missed. Get good quality gear you can move quickly with and practise, practise, practise before you go.