Hi Cindi, welcome to the Cameralabs forums!
The print size is dependant on the resolution of the camera, so if you're comparing, say, 10 Mpixel DSLRs, their images will all be able to be enlarged to the same degree before you start noticing a loss in quality. So in this respect, the Sony A100, Olympus E-510, Canon 400D, Nikon D80 and Pentax K10D are essentially on a level playing field.
What sort of size prints did you want to make, and from what distance will they be viewed?
You're right to consider a model with anti-dust and anti-shake, but there's no one camera that's necessarily better for landscapes or wildlife, or indeed most other types of photography. They'll all be equally good for most types, although if you want to zoom-in a lot on wildlife, you'll need a powerful lens - so you'd either be looking at, say, a 70-300mm in addition to a normal (say 18-55mm) kit lens, or a single superzoom like an 18-200mm which does it all.
Also while the Sony A100, Olympus E-510 and Pentax K10D all have built-in anti-shake, the other manufacturers offer it in optional lenses, and there's pros and cons to each system. If it's built-in, it'll work on any lens you attach for free, but you won't see the stabilising effect through the viewfinder - you just have to trust that it's working. If it's built into the lens though, you will see the reassuring stabilising effect through the viewfinder, but you'll have to pay for it on every lens you want it. Swings and roundabouts really!
As for anti-dust, none of them work 100%, so you will need to get used to using a blower from time to time - see here:
http://www.cameralabs.com/workshops/dsl ... age3.shtml
So really any of the current crop of DSLRs will do what you want, so it's a case of weighing up their differences in features, price, and crucially their look and feel. I'd strongly recommend going into a store and picking up a selection of models, looking through the viewfinder, pressing the buttons and taking some shots. I guarentee one or two will feel MUCH better to you than the others, and these are the ones which should go to the top of your list!
The budget DSLRs we'd recommend right now are here:
http://www.cameralabs.com/buyers_guide/ ... DSLR.shtml
Hope that helps!