It's not as hard as you think, and the benefits are amazing. You only need three resources:
MacVim - Vim on steroids... for the Mac. Most importantly, it gives you the mouse, arrow keys and Apple keyboard shortcuts back.
Janus - A bundle of plugins that make Vim really easy to use and quite similar to ST/TM (like comman+T to jump to a file, or Shift+Command+F to search the project).
PragProg's Practical Vim - A great intro and in depth set of lessons to learn Vim.
You'll experience a week or two of slightly less productive programming, but after that time, you're ability to edit text will soar.
If you ever work on servers, you'll now have the same text editing experience on the server as on your desktop, no need to switch contexts.
Give it a try!