My two cents: I've written six screenplays, none of which have been produced. Writing the screenplay is not the most difficult part, provided you have a good idea for one. The real challenge is getting someone who can produce it to read it. However, having said that, far be it for me to discourage anyone from doing it.

The screenwriting software I recommend is Movie Magic Screenwriter, the official screenwriting software of The Writer's Guild, East. It also contains the formats for writing: Teleplays, Stage Plays, Sitcoms, Novels, Multimedia, Comics, and more. It's avaialable on the Web for about $200 (perhaps a little less). I just bought an upgrade for $90 recently, but you have to own a license in order to purchase an upgrade.

I found some books very helpful. Among them: "Story Sense", by Paul Lucey, "Writing the Script," by Wells Root, Lew Hunter's "Screenwriting 434", "The Whole Picture", and "Screenwriting", both by Richard Walter.

Good luck, gnu.
DougR