This has been a nuisance for me since I started using a Mac but only today did I finally spend the time to figure it out. I found a post that has almost everything you need but leaves out some key details and the direct download link is dead. I’ve recreated the file and you can install it automagically like this in a
wget http://blog.timmattison.com/static/vimrc-2009-03-07 -O ~/.vimrc
This will nuke your existing .vimrc if you have one so save it first!