According to the Apple page on the new "iPod Summary" feature, "you can also allocate capacity to specific types of content". How do you do this? Before iTunes 7, there was a page in the iTunes Preferences where I could set the amount of space allocated to audio vs. data on my iPod shuffle. That page is gone in favor of the new Summary page. But how do you change the allocations? What needs to happen in order for the Apply button to become enabled?