You can publish your iMovie 09 project directly to YouTube, provided you have already set-up a YouTube account & password. If you have not done so, you can sign-up for a YouTube account here.
In iMovie 09, go to the Share menu, and select YouTube…
If this is the first time you have used iMovie with YouTube you will need to click the button to Add… your YouTube account to iMovie; otherwise select your account from the drop-down list.
Enter your YouTube password, a category, title, description and tags.
Under Size to publish, choose Medium.
So that the world can admire your handiwork, UNCHECK the box marked Make this movie personal.
Click Next, then Publish.