I have a Nikon D70, and I absolutely love the thing. Best camera I've ever owned. Even though it's a few years old, it's still a marvelous beast. 5MP is plenty for 8x10 and 11x14 prints, and I seldom do much cropping, so I'm perfectly happy. Easy operation, but allows as much manual control as I want. Great colors, excellent contrast, and amazingly-fast electronics. Ready to snap a pic in less than 1 second. When I bought it was $1k, which was more than I had ever spent on a camera, but it took about an hour to realize that it was worth every penny.
If you're starting out, I'd suggest the same thing as the others, look at the lenses and prices of Canon and Nikon, and pick which ever 'system' fits your needs best. Do you have friends that have a Canon SLR? An old uncle that has tons of old Nikon gear? That might be a factor as you could share lenses with them. I took a peek at Nikon's page regarding D40 lens compatibility...
D40x:
"Nikon F mount with AF coupling and AF contacts Type G or D AF Nikkor: 1) AF-S, AF-I: All functions supported; 2) Other Type G or D AF Nikkor: All functions supported except autofocus; 3) PC Micro-Nikkor 85mm f/2.8D: Can only be used in mode M; all other functions supported except autofocus; 4) Other AF Nikkor*¹/AI-P Nikkor: All functions supported except autofocus and 3D Color Matrix Metering II; 5) Non-CPU: Can be used in mode M, but exposure meter does not function; electronic range finder can be used if maximum aperture is f/5.6 or faster; 6) IX Nikkor lenses cannot be used
*¹ Excluding lenses for F3AF"
Ok, most modern current lenses are AF-S or AF-I, and those should work perfectly with the D40. But a few lenses are still 'D', like the 50mm 1.8 that I mention below. That's a bit of an issue because the autofocus won't work. Otherwise it's fine. Nikon's image stabilization stuff are 'VR' lenses, and I don't see anything that would indicate that these wouldn't work with the D40, but I would be very careful about this. I'd try to email or talk to Nikon directly for clarification. My advice might be either make darn sure the D40 will work the the lenses you want, or to just save your pennies or bite the credit-card bullet and bump up to the D80.
When you buy an SLR, you're buying much more than just the camera, you're investing into that company's products. Canon and Nikon are the most established brands in the 'pro-sumer' area, so you can't go wrong with either.
As far as lenses go, I don't really know much about Canon glass. For Nikon, you can't beat the simple Nikkor 50mm 1.8 ($100) for razor-sharp optics and wide aperture. No zoom, so it's all about composition and optics. For dimmly lit museums where flash photography isn't allowed, you can still get great pix without necessarily needing a tripod. Really superb lens for next to nothing.
For general purpose, I have the 'kit' 18-70 lens and it's great except for a slight
vignetting problem when it's wide open (dark corners). Very quick focusing, and takes lovely shots. I would check out the newer 18-135, as that will give you a nice top-end zoom. I also have their common and cheap 70-300mm lens, and it's just fine for what it is. Not the greatest and takes pretty soft pix, but it's certainly a darn long lens on the D70 (105-450mm equivalent)
I used to have a Sigma 28-300 on my old 35mm film Rebel, and it was a fine lens for most things. Nothing wrong at all with 3rd-party lenses, and some of them are very good, but I like the look and feel of the name brand ones better. I know from first-hand experience that the name-brand lenses hold their value better than the Sigma/Tamron lenses, should you ever decide to sell lenses.
If this is a 'once-in-a-lifetime' sort of trip, I would try to have a good wide-angle lens. I'd rent or borrow one if need be. On most digital SLR's, there's a magnification factor. The way the optics work magnifies the image compared to a traditional 35mm SLR. At least on the D70, the lens multiplication factor is 1.5x, which means that a 18-70 lens actually acts like a 27-105mm lens, this can be a problem for wide-angle shots, as 27mm isn't really all that wide. I doubt you'll ever feel a wanting for more telephoto, but I do for wide-angle. So, even though 18mm sounds pretty wide-angle, it really isn't. I'm thinking landscapes, cathedrals, etc; you're going to want some panoramic, wide-angle shots and from my experience that may be tricky with just an 18mm low end. The 12-24mm Nikkor would be awesome, but that's a $900+ lens.
Enjoy the camera and enjoy the trip. Just make sure you get the camera way before the trip so you can take a few hundred shots first and learn how the camera works!
