You can encode it to a smaller size, using a codec with higher compression (this will undoubtedly lose some quality). It's under the "export" menu command of QT Pro. If you don't have QT Pro, there's a free alternative called QT Amateur (All the functions of QT Pro are freely available in the QT programming API for any who is willing to write the interface, but since QT Pro is such a low price, not many are).
Media Cleaner and similar apps offer more "powerful" compression, due mostly to preprocessing algorithms like "noise reduction," but these are pricey features.
Video encoding is an art form, and you could spend years agonizing over the best way to do it. If you just want to "make it smaller," use h264 (or if the recipient has an older machine, mpeg-4) at about 85% of the quality slider, and scale down the dimensions as far as you're comfortable with. And don't forget the audio (use mpeg-4).