If you have read my other post about Timeline - one of Facebook's new features announced at F8 - you probably cannot wait to get your hands on it! I have some good news for you; while Timeline doesn't officially launch for the general public until the 29th of September, you can get it right now!
Just follow these simple steps:
1. Log into Facebook
2. Enable developer mode by typing “developer” into the Facebook search box, click the first result, and add and 'allow' the app.
3. Head into the developer app.
4. Create a new app (it won't be a real app so don't worry). Give your shiny new app any display name and namespace you see fit. Read through and agree to the Platform Privacy agreement.
6. Look for the “Open Graph” link and click the “Get Started using open graph” option. Create a test action for your app, like “read” a “book”, or “eat” a “sandwich”
7. This should take you into an action type configuration page. Change a few of the default settings (I didn't change anything apart from entering required information)
8. Wait a few minutes...
9. Go back to your Facebook homescreen. An invite to try Timeline should be waiting at the top of the page
If you have any further questions, please feel free to contact me on Twitter, @GMacf33, where I'll be happy to help.