You don't need a lot of megapixels for posting images online. My 6MP d40 produces 3008x2000 images, which is a lot more than can fit on a standard computer monitor. Another way to look at it, a 1280x1024 monitor is only 1.3 MP.
As others have said, lighting would be the most important thing... Some off-camera flashes and umbrellas would be a good start.