Copyright is a deliberately vague issue accorfing to governmental guidelines. There are so many facets to it, from imagery to literature to music, etc., that there are actually very few concrete guides to follow.
However, there is a very simple way to get started. Simply type © 2004 and your name on your documents, and voila, an actual legal copyright has been created. However, what can become difficult is defending said copyright. Usually the basic notation will ward off any plaigarists, but if someone really wanted to try to steal your stuff and you ended up taking it to court, you might have a bit of protection by mailing yourself a copy of your copyrighted script. That way you would have a sealed envelope containing your original materials, and a postmark to help corroborate the date. Its hardly airtight, but my father actually won back-royalties on some of his work by doing just this one simple thing.
As far as attorneys etc. go, you probably don't need that level of protection unless you're planning to play with the big-boys (ie. IBM, Coca-Cola etc)
Ultimately you don't want to spend a million dollars protecting a work that ends up only being worth a thousand.
I have 5 shows that I've co-written for schools that I've simply put the © symbol on. I've had no problems controling the material, even when licensing others to perform it.