It seems that you have some questions about the setup if you get a new Slingbox PRO-HD.
The short answer is that you have to run the whole Setup Assitance for Internet Viewing. Why? Because every time you connect a network device to your router, it will provide a new IP address for the new device. This means that your Slingbox will not work with the IP address provided by the router for the old Slingbox.
Due to this situation, you need to connect everything as you did before with the old Slingbox. Then, you must reset the Slingbox for 30 seconds and wait until the Slingbox gets solid lights. At this point, you will be able to run the Setup Assistant for Internet Viewing. I recommend you to run the Manual Configuration. Finally, the Slingbox PRO-HD will work fine with the iPad 2. The following articles will provide you with the steps to follow:
Once you finish this process, you will be able to get the connection through www.slingbox.com
Hope this helps!