I'd like my mac to monitor a specific folder, say 'TV Shows' and if a new file is added I'd like it to automatically put it into iTunes under TV shows, is this possible or is anyone aware of an application / script that will help me achieve this?
This is very easy to do with automator or an applescript. In automator create a custom workflow, add the action "add songs to playlist". You can then "save as a plugin" of type "folder action", make sure you set the folder you want and enable folder actions!
edit: on another note, remember that itunes does not support many common tv show formats eg .avi files. For video files that itunes refuses to import natively I use a program called VideoDrive