1. Install LauncherPro (free version available in the market)
2. With LauncherPro running.....
3. Press/hold on homescreen...
4. Choose shortcuts
5. Choose Activities (has the yellow LauncherPro icon next to it)
6. When the activities list opens, scroll all the way down to Universal Inbox and click it...
7. A sub list will open showing Universal Inbox and Edit Universal Inbox.
8. Choose Universal Inbox
9. You have now placed a shortcut that will open the Universal Inbox on your homescreen.
I was able to do this just now but if you have just installed LauncherPro, you may need to check the options if some of these steps don't match on your device. Good Luck