I was under the impression that when you sent a video via mms it was automatically resized, but I may be wrong. You may want to visit Motorola Droid 3 - Android Forums and see if anybody there knows if there is something on your particular model phone.
Welcome to Android Forum. I'm not sure of how the Droid works - but this is worth a shot. Open the camera app - Tap menu - then video quality - from there the wording might be a little different on your device than mine, but look for mms-(176x144) or something close to this. Check or enable it - depending on what option you get to turn it on. You now should be able to send video(s).