R.P. (And others that are unable to embed a youtube video)
Copy the URL at the you tube site.
Hit the youtube box above the dialog section. Lower left hand corner of the various option boxes available.
Paste the URL in the script prompt when it pops up.
Delete the part of the URL that ends with the "=" sign, and everything to the LEFT of it. What remains is the actual Youtube ID.
Hit preview to make sure you deleted the correct portion of the URL. It will appear "embedded" in the preview if you did it correctly.
This explanation is longer and appears more complicated than it actually is, you will discover.
[strike]www.youtube.com/watch?V=[/strike]NliGpftosbE
The section that I have "struck" is the section you DELETE