For each Source/Library item (Music,Movies,Podcasts) you want to open with a shortcut, create a new Applescript as follows
tell application "iTunes"
set view of front browser window to (get some playlist whose special kind is Podcasts)
replacing "Podcasts" with "Music” or "Movies", and save it with to your ~/Library/iTunes/Scripts folder (if this doesn´t exist, create it!), giving it an unique name (like "show podcasts","show movies").
Next, open "System Preferences">"Keybaord">"Keyboard Shortcuts" and select "Application Shortcuts". Click on the little "plus" button to add a new shortcut with:
Menu Title: show podcasts —this has to be exactly the name you gave your script
Keyboard Shortcut: <press your desired shortcut, eg. "cmd+2">
Now pressing "cmd+2" (or whichever shortcut you defined) while being in iTunes will open the Podcast library item.