Sounds like you need some kind of compression there. Compression in video is achieved through codecs (short for compression-decompression and is generally a lossy process - the compression technique generally involves discarding data. Don't worry, its totally non-destructive with respect to your existing files).
So, depending on what you intend to do with your video, you have a few options available. For distribution of short home movies on the internet the current defacto standard is WMV. For larger movies files distributed over LANs, the standard is either DivX, Xvid or occasionally RMVB. Finally, for use on standalone DVD players, you'll want to make a DVD (or variants of the DVD standard called VCD and SVCDs which fit on CD-R media and can play in most DVD players). For these fomats you'll need MPEG2 (DVD and SVCD) or MPEG1 (VCD).
The creation of DVDs and VCDs is a whole process in itself. Phew, started to go off on one there. Think I need to update my guides at
www.marcpeters.co.uk so I don't have to write such long posts
Hope I haven't caused you to ask more questions than you thought you had!!!