I have been reading a lot about this recently and it has intreged me.
there was Project Orion
was scrapped in 63' because of the The Partial Test Ban Treaty of 1963
http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion )
PROJECT LONGSHOT. This says it would take 100 years...
I Have read a lot recently about Alpha centuri having a planet that's identical to earth.
i qquote
On January 15, 2010, a team of astronomers released the results of computer simulations indicating that kilometer-size planetesimals can form and accrete into rocky Earth-size planets around...