Download MacTheRipper. That helps you rip the DVD onto your comp. Just click "Go" when the DVD loads. Wait a while for it to finish and it will create a virtual DVD on your HD with the same title as the disc.
Then download Handbrake, and open (in Handbrake) the virtual DVD that is now on your HD. You can select the AppleTV Preset. This will create an mp4 file that you can then import into iTunes.
When you import it into iTunes, it will show up as a Movie. To get it into the TV Shows section, click on the file and press "

" key and the "i" key at the same time. Click on the Video tab and change it to TV shows.
To get individual episodes by themselves, open the DVD in the DVD player, and click "Window" in the menu bar, and make sure "Navigator" is checked. Go to the episode you want and write down "Title" and the various "Chapters" that that episode uses (something like Title 3, Chapters 1-9). Bascially each commercial break will be the start of a new chapter, so you'll have to fast-forward to get them all. You can use these in Handbrake to only extract that one episode- just select the proper Title and Chapters in the drop-down box.
Once you get comfy with this, you can create smaller files by changing the Average Bitrate setting in Handbrake to something lower than 2500 (but this reduces quality). Make sure to name each episode something different in Handbrake...or else it will just keep overwriting the one file.
It's not necessary to use MacTheRipper, since Handbrake will work with the DVD in your drive. But I and a lot of people prefer to use MacTheRipper anyways since it will likely convert faster if it isn't reading from your dvd drive.