does anyone know if I can buy a regular airbrush or if it has to be a special kind. The ones that ive seen pictures of look like the ones they sell at the craft store.

The airbrushes are pretty universal. Most any kind will work. There are a few made especially for cake/cookies, but it isn't necessary to buy one of those. However, the compressor is very important. Most commercial compressors are too strong and the air will blow holes in your cake. You need one that has very low psi.