Hi Danielle,
If you want to add videos to your iPod, they'll need to be in either mpeg4 or H.264 format. Have a look at the thread below, there's info & links for downloading free converters (if you don't already have one). I have Win XP & use the 3_GP converter. Videora's another popular one. For Mac, someone recently said that iSquint works well.
How to transfer music to my iPod (& iTunes)