You are buying a digital camera.
You will soon use it almost everywhere, not in just your planned application, so think wisely. Not that once the 3-CCD sensors arrive it won't be a whole new game. At least your budget is sensible for a "starter" camera. Like a "starter" home or "starter" wife.
Anything over five mpx is adequate for 11x14 enlargements and gives you plenty of redundancy in cropping - something we take for granted with film. You can, of course, use a product like Genuine Fractals to interpolate pixels in an emergency, and it is pretty good at making stuff up. I use it to "enlarge" images that clients send for backgronds that never have enogh pixels...
Newer cameras not only provide more pixels, but make images that are "quieter" to use a video term - roughly comparable to film grain. This is very important because noise interferes with the camera's ability to deliver deep color tones - especially in dark areas where professionals make their images look so rich. And a new camera with high resoution takes better low-res images, too.
At MacWorld Boston I met some fellows who make QTVR for their living. There was a great show of work from the International QTVR association:
http://www.iqtvra.org/iqtvra/docs/en/index.php
and one of their members is travelling extensively to make QTVR for the Smithsonian.
What I learned was that individual images in a panorama don't need to be all that well-resolved, but assembled, the files can get huge. The Smithsonian guy has a pro Nikon that makes only 4Mp. It is last year's design. Plenty of pixels since his images will be nine shots merged.... 30 megatrons or so.
To answer your question obtusely - it isn't the number of pixels you want, it is how many your equipment can manage. It still takes a long time for a high-resolution image to load and this can mess-up a presentation..... I do many small LCD projections in my work. Fluidity is more important than detail. If I need to show a detail, I prepare a proper detail view and cross-fade to that.
Sooner or later every viewer hits the disappointment distance - like walking toward a woman with great hair until you realize she is Methuselah's widow.
You must go-to-the-end-and-then-come-back on this one because only you know how much redundancy you want to be carrying around - getting ready for that really large presentation some day - and the clerical fallout of hard drive storage and archiving we all struggle with.
Also compare how the camera feels, its bulkiness [newer cameras are losing the original digital elegance, bulging with tumor-like lenses and knobs], the type of memory - Sony has proprietory memory and I hate that - compact flash is my hero - and battery life. Also essential is lag time - warm-up time and shutter delay - The new Nikon D70 is instant-on - first reasonably priced machine to do that. I also hate those cameras with the zoom lenses that grow dramatically from the front of the camera body. I often get one of these in my hands while photographing tourists "all together??"
I have several jokes about this:
First, when they are handing their camera to me, a stranger, I say "I am almost certain that I cannot run faster than you, so this will be okay." They laugh.
And when I finally have the camera, I mess with the zoom. If it sticks out dramatically, as the tourists are assembling themselves into a grouping that approximates friendship, I loudly announce, horrified :" Watch out! It has seen a female of its species!!" Any woman that laughs at that one I talk to later.
Dwight Atkinson