Well, even if they had managed to harness the power of a moped it's likely that they would have also encountered radio waves before. Anyhoo... http://en.wikipedia.org/wiki/Intergalactic_travel
That all depends, First of all where are they from ? Another planet, another dimension or maybe even another time ? Let´s think outside the box for a minute, there are various ways of getting from A to B, A few methods might be the use of wormholes, the ability to bend time and space around the craft, quantum tunneling, time travel, etc etc. With the vast distances in our universe, i don´t think light speed is going to cut it.