I apologize, I wasn't exactly as clear as I could have been.
What option are you exporting your movie as? When you choose the "Share" option to export it, you should see things like "Web", "E-mail", "CD-ROM"...etc.
One of those options would be "Expert Settings"... choose that one.

Then select "Movie to QuickTime Movie" and hit the "Options" button.

In the "Movie Settings" window that comes up, click the "Settings" button.

Another window will open and you will see "Compression Type" at the top with a drop down menu.
Choose "Animation" from the menu.
In this same window under the Motion section, set the frame rate for 29.97 fps
Under the Compressor section, set the Depth to "Millions of Colors+", then set the Quality to "Best"
Now hit the "OK" button on this window.

Back at the "Movie Settings" window, click the "Size" button.

This will open the "Export Size Settings" window
From the Dimensions drop down, choose the setting for your screen size.
(Standard TVs will be the default NTSC standard of 720x480)
Then hit "OK" to close this window.

Again, you are back to the "Movie Settings" window.
Now uncheck the box where it says "Prepare for Internet Streaming" and hit the OK button to close this window.

Now, you are at the "Save Exported File as..." window.
Name your file and save it where you would like to.

This will take some time to render, so leave it go until it is done.