Know-How Exchange : SEO/SEM

We would like to change the name of our website (primary URL) to our secondary URL (a similar name) which is already ‘pointing’ to our current site. Can this be done without losing our current SE listing position and page rank? We are running a small PPC campaign with Yahoo only, but would like to start publicity and other campaigns but obviously want to promote our new name. Do we have to start all over again or is there a way to make a smooth change over? Would appreciate some advice from the wealth of knowledge out there. Many thanks.