Can i get better resolution on old blurry video clips using iMovie 11 or QT? For Dummies, hah!

I am trying to get better resolution from old somewhat blurred TV video clips that I have downloaded from tube. These are usually 4-5 minute clips from the 1970's. I do not have any source material tho. If not able to clear up in iMovie is there other app. that can be used and which is best for this purpose? I'm new to video editing so explain answer for dummies!