OK, any camera nuts out there?

Here's the deal - I'm going to be getting a belated Birthday present for myself - a digital SLR camera. I've been reading reviews, going over my budget, and I'm down to a couple of choices - the Pentax K100D, and the Nikon D40X. There are pros and cons to both of them. I've owned both Pentax and Nikon film SLR cameras in the past, and I've been happy with both of them. I don't have any sentimental favorites. So here are a few questions for anyone who knows the answers:

How much of a difference does 10.2Megapixel make vs. 6.1Megapixel for someone who is not a professional photographer? The Nikon D40X is 10.2MP, and the Pentax is 6.1MP. I've had some work published, but I've never gotten paid for it. It's not what I plan on doing for a living either. I don't see my photos getting blown up and placed on a NYC building. I wouldn't mind getting a photo enlarged to 14X11 or 18X22, but I'm not going to be making any posters.

Does anyone know how sturdy they are? I'm not a gentle guy; I take care of my gear, but I do a lot of traveling (I'm in the military) and any camera I own would have to travel with me. It would not have a cushy lifestyle. Chances are it would end up in the desert for a period of time.

What, if anything, would cause you to purchase one camera over the other?

I welcome any input. This is going to be my Birthday present/Christmas present/Anniversary present all rolled into one, so I'm giving it some thought before I shell out the bucks.