There are no shortcut keys to select the Music, Podcast, TV Shows, and other libraries. But you can use AppleScript to create some. Here's how:
What you'll end up doing is creating a small script for each of the libraries you'll want to access. Here's the script for the Music library:
tell application "iTunes" try set view of front browser window to (get some playlist whose special kind is Music) end try end tell
Some might suggest using this syntax instead:
set view of front browser window to playlist "Music"
That's fine, too. I just prefer using special kind to avoid any ambiguity. Save that as "select_music.scpt" in your ~/Library/iTunes/Scripts/ folder so it will appear in the iTunes Script menu. Now, assign the script a "Command-1" keyboard shortcut.
I think you can see where this is going. You'll create a "select-movies.scpt" and assign it "Command-2", and so on. The special kind parameters for other libraries are Books, iTunes U, Movies, Podcasts, and TV Shows. For other libraries you may have to use the name parameter.