Preparing to re-install Os x.

So here's my deal, my mac is wigging out and after running TONS of hardware tests, rebuiliding my directories and all sorts of things the only fix I've found will be to re-install os x. All I need to know is, how can I make a back up of all my programs and such so that once it's re-installed I don't have to re-install tons of things? I'd rather not have to reset all my prefs on programs either like how firefox has all my passwords saved and little snitch has a crazy library of connections to monitor. I'm sure this is a novice question but I just need help

Assuming you're at least running Leopard, the best way is to use Time Machine to make a backup to an external hard drive. Upon reinstalling, you will be asked if you have a backup. Make sure your Time Machine hard drive is attached, reply yes, and it will restore all your apps, documents, music, photos, settings, etc.