It depends on the format you save it as. This goes true for video,sound and pictures. Bitmap are large picture file, while jpeg are smaller. The larger the better the quality and vice versa. I'm not sure what's the largest video format, maybe it's DVD or HDTV but I'm not sure (maybe someone can tell you), and MPEG and avi are probably smaller video format. MP3 are small sound format (I think wma is much smaller) while wav are larger.
If you're into multimedia editing, I suggest you have a decent machine with atleaset P4 3Ghz or AMD 3200 1GHz with 1GB of ram (2 GB recommended) and 250+GB of harddrive space (more is better), and a mid-range video card, and 5.1 surround sound with like 70 watts speaker package.