In my opinion, I would submit the title as a TV movie. The title page can be reformatted if the pilot becomes a series. Perhaps an IMDb representative or another contributor can verify if some stand-alone pilots are listed on IMDb as TV movies or any other categories.
Please write back if you have any more questions or concerns. I hope this helps.
GMJ's advice is correct, assuming that this show is only at the pilot stage as yet, and you are not trying to add a pilot episode to an existing series?
Col Needham, Official Rep
The new title submission form can be reached through -> http://www.imdb.com/help/show_leaf?titletopfaq