I've already tried deleting the pref. file,
You found it in the right Library - Not the one on first window on Start-Up hard disk - but the one in Your User account. Hidden if You use Mac OS X.7
I've got plenty of room on my hard disk,
Only the Start-Up hard disk is of interest - my minimum is 25Gb free space
If You have any External Hard disk You use for VIDEO - It/they must be Mac OS Extended formatted - UNIX/DOS/FAT32/Mac OS Exchange works for most other things but not for VIDEO - they breaks the video file beyond repair.
and I'm not sure how you run repair preferences.
Run Disk Util tool and to the left select Your hard disk - now under the big white area to the right You read
Control Permissions and Repair Permissions - AND Control and Repair Hard Disk
To do the last ones Your Mac need to be started from DVD or other hard disk. Can not do Brain Surgery on one self.
I'm not to sure about the corrupted movie project thing.
Start a new iMovie project (Plus sign under Project Library) and put in one clip at a time and see if all works OK - If it starts to ill behave then last included clip might be the problematic one.
Yours Bengt W