I had the same problem. In your iTunes library, highlight the files that you want to categorize as something else (ie, select all the files that are TV Shows). Right click and select the first option, "Get Info". Click on the "Options" tab. There will be a drop-down box where by default, iTunes categorizes all video files as "Movie". Just hit that drop-down and select TV Show. Use this method for each category you're looking to file your videos as.
*EDIT* It's the third selection down on the "Options" tab. It's a checkbox and a drop-down box and it says "Media Kind".