Close, but not quite. Einstein's _theories_ show that nothing with significant mass can travel AT C. If you look in depth at his equations, and work done by others, the graph has a symmetry line/asymptote at C, with things at greater speeds than C not able to slow down to C. So this means that slower than C is OK, faster than C is OK, velocity = C is a no-no for anything with significant mass. More recently, physics doesn't assign the term "Law" until it can be determined that it works for all (or almost all) cases. Newton's Laws were shown to have a high degree of error in high gravity environments, or when travelling close to the speed of light. It is somewhat difficult to directly test Einstein's Theories at this time, but from observations the theory seems sound.
At this time, we can only consider travel within the solar system. As far as in-solar system travel, light sails would work, but only after getting off the Earth's surface (even if using Lasers). Getting off the Earth has been the biggest problem, now if we were to develop some type of Electrodynamic Tether, getting to LEO would be simple. The Ion drive used on Deep Space 1 has an ISP of ~3100. Pretty darn good. Even better is Project Orion, a concept project thought of in the '50s and '60s. Orion had a theoretical ISP approaching 10,000. The only drawback...the concept used explosions from nuclear bombs that were dropped off the back of the ship. Not exactly something you would want to use near an inhabited, technological planet.
This is not to say that we won't find some way to other stars. It probably won't happen within my lifetime, but look at what has happened in the last century. From the time of the first human flight, we have split the atom, made destructive devices powerful enough to annihilate technological life on the planet, developed ICBMs to deploy those wepons, used those ICBMs (and their descendants) to mount several trips to orbit and the Moon (mostly because Kennedy needed some PR fodder to point the public away from the non-existant missile gap he ran on, and as a Prestige thing...beat the "commies"). We also developed the Internet to organize the developemnt of such projects (Thank you ARPA, not Gore), and stealth technology, GPS, smart bombs, etc. We have even approached the verge of quantum computers and scientists have taken particles of light, destroyed them and then resurrected copies more than a mile away.
I have learned, in my 1/4 century on this planet, not to underestimate the drive of the human spirit. I can't say for certain that we will or will not ever leave our solar system. I can only hope that we learn how to do so before we either destroy ourselves or before this planet becomes uninhabitable because of some natural phenomenon. I would expect any solution to look like something impossible to us at our current technological level, but look like child's play to our descendants. Just like Einstein's peers scoffed at the Patent officer's ideas, until they saw the light from a star bent around the Sun during a solar eclipse.
Mike Gerszewski Univ of North Dakota Space Studies Graduate Assistant NAR #80579