A guide has been posted my MacRumors on how to install iMovie on the first generation iPad, what's more, you do not require a jailbreak to get this to work. Follow the steps below to get it on your own iPad:
- Download iMovie from the Apple App Store.
- Download and install the latest version of iPhone Configuration Utility (Windows | Mac).
- Start iPhone Configuration Utility, click Applications from the left and open iMovie (iTunes> Mobile Applications)
- Nwo connect your first gen iPad using your USB cable and select your iPad listed under Devices.
- Select Applications and Install to install iMovie 1.2 on your iPad.
That's it, you should now have iMovie running on your 1st Gen iPad. Any questions you may have are welcome in the comments section below: