I'm a genie, drewprops!
All SLR cameras are compatible with Macs, because Macs are hugely popular with photographers both pro and amateur.
You say you want 10 megapixels, and most DSLRs have at least that pixel-count these days, but other things affect image quality to a greater degree. Lens quality is hugely important, as is dynamic range and signal-to-noise ratio. Technique is most important of all.
Olympus SLRs are based around the Four Thirds System, with smaller sensors than most of the competition. One of the benefits of this was supposed to be much smaller cameras and lenses, but that hasn't really come to fruition. However the lenses are very good, being purpose-designed for digital cameras with the Four Thirds sensor. The cameras are also excellent in terms of build-quality, value, and ergonomics. General image quality is excellent but the cameras have slightly more noise (grain) at high ISOs than the competition, and slightly less highlight range (meaning bright areas in the photograph are more likely to "blow": record as pure white with no detail). If you want an Olympus a good place to start would be the E-520 model, usually sold with one or two lenses in a kit.
Nikon make well-rounded cameras that have few obvious weaknesses, but they aren't the cheapest cameras (or lenses) on the market. However, they're strongest versus the competition in the $900 and up range (D90, D300, D700, D3), and the very bottom of the SLR market (D40). The D60 which straddles this range is an excellent camera, but arguably out-specced by models from all the major competitors: Canon, Pentax, Olympus and Sony. That said, I bought a D60 not long ago, because I see little value in Live View (being able to compose photos on the rear display, like a point-and-shoot camera, rather than only with the optical viewfinder), and because I really wanted the Nikon F-mount for the wide range of older and third-party lenses that provides.
The Nikon D90 that pscates2.0's dad has is of particular interest because it's the cheapest DSLR that can shoot video (and it shoots High Definition video no less). It's also an extremely impressive camera in its own right, but it's not $700.
Canon make a wide range of appealing cameras from entry-level to ultra-high-end. Their cameras are known for their great sensors, with low noise and good dynamic range. However in the last year or so the competition has closed the gap and in some models exceeded Canon's sensor performance. Because a large part of Canon's competitiveness was based on their sensors, Canon perhaps didn't develop the rest of the camera (ergonomics, metering, useful new features, etc.) as aggressively as they should have. The low-cost Canon SLRs feel decidedly cheap, even though they provide superb photographic results.
Pentax make great cameras and lenses although they don't have as wide a range of options as some others. They're aimed more at photography enthusiasts than casual snappers, with fewer gimmicks and more concentration on things that appeal to experienced photographers, like weather-sealing, good build quality, and excellent prime (fixed focal length) lenses.
Minolta no longer exist, having been bought out by Sony. The Sony DSLRs build on the Minolta heritage, with the same lens mount (for compatibility with old Minolta lenses) and a strong emphasis on innovation and value for money. The system is still in rapid development, and is likely to become a serious competitor to Canon and Nikon at the high-end in the next year or two. Their entry-level cameras are loaded with features and priced extremely aggressively, to help Sony gain market share in this new arena.
Go to the websites of the manufacturers and have a look their marketing blurb, then check prices on B&H or Amazon to get an idea of what you can afford. If a model catches your eye, check out a review of it at
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