An iMovie project is a text file in hexadecimal that contains instructions for creating your edited movie. The movie is created when you use the SHARE menu by running the instructions in the project.
The project instructions will reference the actual video files which are contained in the Events. So if you delete your Event files, your projects will no longer have anything to reference, and they will no longer work.
Once you have shared your project in all the sizes and formats you need, you could delete the event clips. Just be aware that you will not be able to edit the project any further.
I would recommend getting a large external drive, formatted as Mac OS Extended (journaled) to keep your Events on.
This is excellent. Thank you so much for all your help. One last question abou thte External hard drive. On a Windows computer, I have basically added HD's in a RAID configuration to increase capacity in the past. Is this what you are suggesting or is the "Mac OS Extended" simply a Mac formatted HD with all the extra videos on it?
What if I do this later on and simply move all the iMovie events to that external hard drive. Will iMovie automatically register the new path or will I need to add them again?
Thanks again for all your help. I am forever grateful.
The Mac OS Extended (journaled) refers to the formatting. Most Windows disks are formatted as FAT32 or as NTFS. Mac OS Extended (journaled) similar to these.
Mac systems can READ disks that are formatted as NTFS. Mac systems can READ AND WRITE to disks that are formatted as FAT32. Even so, iMovie will not recognize a disk for use in iMovie unless it is Mac OS Extended (journaled).
Sometimes you will see Mac OS Extended (journaled) referred to as HFS+.
You can buy hard disks that are pre-formatted for Mac. You can also buy disks that are preformatted for Windows and reformat them using Disk Utility, which is an App on your Mac in the Applications/Utilities folder. If your Mac supports FireWire, a Firewire drive will give you the best performance for video. You can also use USB drives. (If you are importing DV tape, you must use Firewire (or the internal drive), but you could move it to a USB drive later.) Also, you can obviously use Thunderbolt drives for really good performance, although they are still a little pricey.
If you reformat a disk in Disk Utility, you will lose all data that is currently on it. In Disk Utility, select the Disk, and then choose Partition. For Partition Layout, choose 1 (unless you need more), and under Options, thoose GUID Prtition Table. Give the Partition a name, and choose Mac OS Extended (Journaled) for the Format.
RAID usually refers to combining drives to achieve either fast performance or redundancy in case of failure. You can use locally attached RAID drives in iMovie if they are formatted as Mac OS Extended (journaled).
You can move Events and Projects to an external drive, but the move must be made within iMovie to preserve the linkages.
Here are instructions for moving Projects. http://help.apple.com/imovie/#move7d66613
Here are instructions for moving Events. http://help.apple.com/imovie/#mov3ac6d42c
Here are instructions if you want to move all project assets (video, music, photos) to an external drive so you can edit it on another Mac. http://help.apple.com/imovie/#mov3ac6c7c9