Plenty unless you plan to store video on it. Generally a compiler or two and a bunch of projects will fit within 8-10 gb easy. Add a few hundred snapshots, that's another gig. All your stolen, er, 'backed-up' mp3 files, another gig.
It's only when you want to store your DVD collection or many hours of video that you will get close to that much space.
and... FIVE YEARS? That machine will be a DINOSAUR by then!
:-)