Actually collision is the word that astronomers use, but Sean is right, the stars mostly won't hit each other. Galaxies can, nontheless, collide (i.e. they exchange gas and stars as they pass close to, or through one another).

I've never heard that we may have hit Andromeda in the past (we're both about the same size and a collision would have done some wicked damage to the disk).

However, if you take a look at the large and small Magellenic clouds (our nearest "galaxy" neighbours) it truly looks like they have collided with us in the past - and will do so again long before we get near Andromeda.

Joseph A. Biello
-------------------------------------------------------
Ph.D. Candidate
Department of Astronomy and Astrophysics
University of Chicago
484 Enrico Fermi Institute
5640 S. Ellis Ave.
Chicago, IL 60637
(773) 834 1059