iPhone 3G to iPhone 4

1. How do I pre-order it on June 15th?
When placing a pre-order online, the options are as a new AT&T subscriber with a new phone number, or with porting a number from another carrier. If the latter, you enter your cell phone number and area code for the number being ported.
Or as an existing AT&T subscriber. As an existing AT&T subscriber you enter your AT&T cell phone number with area code. Apple checks your account with AT&T to determine your upgrade eligibility and the price to be charged for your selection - 16GB or 32GB. You provide a credit card number for payment and the credit card is not charged until the iPhone ships. If pre-ordered on the 15th, the iPhone should be delivered on the 24th.
2. Once I pre-order it, do I pick it up on June 24th from the Apple Store (of my choice?) and then take it to AT&T and tell them to switch it over for me from my broken iPhone 3G?
You can have the iPhone shipped to your home or office - someone must be available to accept and sign for the delivery, or delivered to a local Apple store reserved in your name. The Apple store will have a pre-paid line for pre-paid orders along with a regular line for walk-ups.
If delivered to your home or office, you will activate the iPhone with iTunes on your computer. Power the iPhone on and when connected to iTunes, you will be provided the iTunes activation process with AT&T. If delivered to an Apple store, the Apple store can do the activation. You dont need to take the iPhone to an AT&T store for the iPhone activation.
 MacBook Pro 15" Intel Core 2 Duo/2.53GHz/4GB RAM/500GB HD Mac OS X (10.6.3)  iPod w/Video 30GB,  iPhone 3G 16GB