You have the option of setting this pre-order product to be on a limited run by setting inventory levels, or letting as many people order the product as possible by not tracking inventory. Please know that if you do track inventory, and the level hits zero, customers will not be able to purchase the product any more.
1.) Login to your store's control panel.
2.) Either add a new product, or edit an existing one.
3.) Scroll down to Pricing & Pre-Order Options and fill in the radio button next to This product is coming soon but I want to take pre-orders.
4.) Here, you can change the message that is displayed, whether you want to remove the pre-order status on a certain date, and when the product will be available in store.
For example, if you choose June 17th, 2012, in the product page you will be able to see this:
5.) Once you have finished changing the status of the order, click Save & Exit.
To confirm that your product is available for pre-order, there will be a “(Pre-Order)” in grey beside the product's name: