As far as I know, you're out of luck if you want iMovie 1 by download. Apple got everybody hooked on it, then started charging $49 for iMovie 2 downloads.
Your best move is to pony up the $49 (keeping you on the firmest ground, morally speaking) or find another Mac user who previously downloaded iMovie 1 (still firm) or find someone who got iMovie 2 free with their new Mac (shaky ground) or find someone who bought iMovie 2 (just plain thievery).