Yes - BUT there are Must's and Should's
• external Hard Disk - MUST be - Mac OS Extended (hfs) formatted - UNIX/DOS/FAT32/Mac OS Exchange works for most other things BUT NOT FOR VIDEO whatever program used iMovie or FinalCut.
• If You want to save space - You must Copy Project With Event's as Projects are very small text documents conducting/directing how Events are to be played to look like a Movie. There is no Movie in Projects
• Should use a FireWire hard disk - As USB/USB2 performs badly to me especially when filling up.
Yours Bengt W
Within the project library of iMovie you should see your external drive listed along with the projects stored on your mac. To copy a project you simply drag the project from its current position to your external drive. You will then get the option of copying just the project or project and events. As Bengt rightly states you should copy both project and Events. If you hold down the alt key as you drag the project you will get the option of moving rather than copying. I would NOT recommend doing this in case there are problems during the copying/moving process (I don't find iMovie to be the most stable of apps) and you might find the original project has been deleted without properly copying it across. Better to copy to the external drive, check it works ok and then delete original.
Hope this helps.