To get a treasury you need to wait until some of the current lists expire so there are less then 333 lists left. You will then have a window of time to grab a treasury!
Once you have this your can add items as you go along using the item numbers (the same numbers you use to display items in the chat rooms) you get 12 items and 4 reserve items (incase one item should sell).
The only way to find out if you have featured in a treasury is to go to the list http://www.etsy.com/treasury.php and also http://www.etsy.com/treasury_west.php if you can see a star in any of the titles it means you are either featured or a reserve.
Treasuries are picked to go on the front page – so think carefully about what you pick. You are allowed 1 item from your own shop to feature in your treasury BUT if you get picked for the front page your item will be swapped with an item in your reserve. (Treasuries are not ment for self promotion)
All the front pages are stored here http://www.flickr.com/photos/28488923@N05/ just incase you ever think you may have missed your 5 minutes of fame!