http://www.uspto.gov/patents/process/index.jsp
The patent process can be grueling, but don't be discouraged. Even if you think you've found a prior art, don't be discouraged. Improvements upon existing patents are patentable.
Just be sure to document all of your work. And do try to build a prototype and document that, too. As for the actual filing of the patent -- there are awful ways to do it, and there are brilliant ways to do it. So, finding a good attorney is key, and you'll have to ask around.
My personal experience was on closer to the "awful" side of the spectrum, wasting about $20K on an attorney that didn't have a grasp/experience on the type of intellectual property (IP) I invented.
Best of luck!