A couple of quick notes:
* Congratulations on the interest. The 'go away and write a treatment' may just be a blow-off, but it may also be a genuine interest. The only way you'll find out is to write the treatment, which you should do anyway.
*
"then secure it with say the writers guild or something that legally copyrights our idea"
The story is copyrighted from the moment you write it down. For a start, you can't copyright an idea - only your implementation of it. When they insist you register it with the writer's guild (or whatever) first, it is their gesture of good faith - they are making it clear that they aren't trying to pinch your work.
* An example of a successful treatment is here:
http://www.tvwriter.com/resources/star_trek/startrek2.htm
It was written for a Star Trek Voyager episode - from memory the final episode follows it quite closely.
* One technique that I've found useful is to start with a ONE PAGE treatment before expanding it.
Get rid of all extra characters, explanations etc & limit it to a single page.
Review it, pull it apart etc.
* When that single page treatment is OK, expand it (or rewrite it) to be about 6 pages. By doing it as a single page first, it forces you to concentrate on a single thread of story that will avoid the longer one getting confused.
Good luck,
Mac.
(Disclaimer: Take everything you read on the internet (including what I say) with a grain of salt)