Well, these days, "more megapixels = better resolution/quality" isn't strictly true anymore, but it's a tactic salesmen will always use to get you to pay more. What you want for architecture is a wide-angle lens, which are pretty pricy for DSLR-type cameras. There are also wide-angle point and shoots that are better suited for your price range.
I cannot think of a single page on the internet that can help you more than this one: http://www.kenrockwell.com/tech/recommended-cameras.htm I suggest noting what he says about resolution no longer being important, and he also points out a great wide-angle point and shoot that he discusses in depth here: http://www.kenrockwell.com/canon/compacts/sd980.htm.
If you want a DSLR, you can expect to pay at the very cheapest, $400-500 for the body, most likely with a kit lens. (Nikon kit lenses are usually very good, some are downright excellent. Canon's kit lenses in general aren't quite up to par with their stand-alone lens offerings, but aren't terrible.) If the widest angle of the kit lens isn't wide enough for you, wide-angle lenses are generally pretty pricy themselves, and run at least $400+ for the off-brand lenses, (for instance, Tamron makes an excellent wide-angle) and double that for Nikon or Canon lenses. More wide angle info: http://www.kenrockwell.com/tech/digital-wide-zooms/comparison.htm
Now, you'll probably be able to find camera bodies and lenses for cheaper than I've listed here, but you'll often be trading resale value or long-term durability for a lower pricetag up front. You have to figure out what's most important for your needs and base your purchases on that.
As for ISO, it's a measure of how sensitive a camera's sensor is to light. The higher the ISO, the more light the sensor picks up in the same amount of time as another shot at a lower ISO. Unless you're doing nighttime architecture photography (which you would probably be using a tripod for anyway, in most cases) it's not particularly relevant to your area of interest. But if you want a good all-around camera for everyday use as well, any DSLR is going to outperform a point-and-shoot in low-light situations.
Also, lens aperture/f-stop is a measure of how wide the shutter opens, and shutter speed is how long the shutter is open. All three- ISO, lens aperture, and shutter speed- make up the overall exposure of the image.
So, if you want a wide-angle P&S, (point and shoot) I recommend the one I linked above. If you want an inexpensive DSLR, I say look on Ebay and other places for the now-discontinued Nikon D40 with it's excellent kit lens, and see if the widest angle on the kit lens is wide enough for you. http://www.kenrockwell.com/nikon/d40.htm The D5000 is it's current replacement, but it's a few hundred dollars more for not a whole lot more camera. (Sidenote: Avoid the Nikon D3000 like the plague. It's cheap, but for good reason. =/ )
I hope this helps.. I'm sure others can chime in with recommended Canon DSLRs, but I think Nikon's DSLRs offer more value-for-money, so that's where I've focused all my attention. Canon Point & Shoots, however, blow Nikon out of the water on every level.
I've tried not to bore you to tears, but if you have any more questions, I love dragging people kicking and screaming into the world of photography. ^_^
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