500D isn't a "pro" body. However it will make excellent pictures. Correction... the camera doesn't make the picture, it's the photographer. Get a Canon 450/500/550 or Nikon 3100/5000/7000(this one is semi-pro). Skip the bundled kit lens and get something better. Don't worry about "mega-pixels" That's a marketing term invented by the marketing department to sell point n shoot cameras to people who don't know the first thing about picture taking. Anything above 10-12 megapixels is more than sufficient unless you are planning to make wall sized prints.

Anyway, regardless of what what system you go for (CaNikon/Pentax/Sony) spend some time learning the basics of photography, buy one or two good lenses. Don't worry about the body, it will get outdated in no time.

Read the forums at DPreview etc. Most of your questions are answered.

If you want a starter Nikon system I would suggest D5000 + 18-105mm VR lens + 35mm f/1.8 lens.