And, if you can't write to the system partition, you need to remount it RW. I understand Root Explorer will do this, but I couldn't get Root Explorer to install.
From the shell you would do something like this:
mount -o rw,remount /dev/block/mmcblk0p3 /system
cp VideoEditor.apk /system/app/
chmod 644 /system/app/VideoEditor.apk
PLEASE NOTE: The /dev/block/mmcblk0p3 MAY be different for your device. You can run "mount" at the prompt and look for where /system is mounted
Also, it lists in your menu as "Movie Studio" - took me forever to find it because I was looking for "Video"