Just a few days ago, Twitter started rolling out a feature that lets you download all the Tweets you've ever Twittered. We've known this was happening but now Twitter is starting to push the feature to everyone. Here's how to get your old tweets.
Go to your settings, and scroll down to the bottom. There you should see an option to request your archive. Click it if you do, and you'll get an email with with a link to a .zip file of all your tweets.
Download it, and once you open it, ignore basically everything except index.html.
Select that and you'll see a page where you can browse through every tweet in your entire archive by year.
If you don't have the option to get your old tweets yet, be a little patient. Twitter just started the big roll out today, so it will take a bit to get to everyone. Hey and it will also give you a little time to worry about the stupid things you tweeted two years ago when you were out partying. [Twitter]