Your movie camera has recorded 26 frames (still pictures) per second, and that is what is being transferred to your computer. As a rule of thumb you can assume that 1 minute of imported footage will equal about 220 mb (about a quarter of a gig). Extrapolating that to one hour would equal 13.2 gigs.
It is often recommended that you keep at least one disk drive free for nothing other than movies - I prefer to use external drives so that I can move the footage between my desktop and laptop machines easily.
Hope this helps :-)