"The Voyager space probes offer a good illustration of just how daunting the distances are. Sent skyward in the final days of disco, Voyagers I and II hurtled past the outer planets in the early 1990's at a whopping 59,000 km per hour. At that speed, the probes will reach the nearest star in about 60,000 years ?- hardly the stuff of compelling cinema.
To speed the trip up would require a huge increase in fuel weight, which itself would create problems. The amount of fuel required to shorten the trip to the nearest star would be enormous. Even a nuclear fusion engine, one of the most powerful conceivable, would require (and this image is pilfered shamelessly from NASA's Jet Propulsion Laboratories website)
close to a billion super tankers full of fuel to make the journey in a reasonable time. That's assuming you don't want to do anything fancy like come back. Or do it in less than nine centuries. Or see something other than the nearest star."
http://www.scq.ubc.ca/?p=208