If applying to test on iPhone/iPod, what's your iPhone UDID?
Providing your UDID allows you to install beta applications that are not yet available for purchase in the iPhone store. You can access it by selecting your device in iTunes, clicking the Summary tab, and selecting the 40-character "Identifier" that appears (you may need to click "Serial Number" to reveal it). Command+C on the Mac will copy it so that you can paste into the form with Command+V.