There is no official way to do that. The calendar is a built in application, and is configured as to how Microsoft deems best according to the research and usability studies it has done.
What you can customize in the calendar (sorry, nothing for the live tile)
- The color for each calendar
- Show to-dos
- only show facebook events for those you have responded to.
- selectively turn off calendars for an account.
Sadly, you cannot customize the calendar tile. If someone knows of some homebrew application they can post in the comments. But you will have to have your phone rooted and/or developer unlocked to do it.
If you are looking for a 3rd Party app, I see a few in the Marketplace (just search for calendar).
Live Calendar (4 stars from 89 reviews) looks like it might be what you are looking for, but I haven't used it so I can't vouch for it being awesome or actually consolidating event's from your accounts. It may just be another calendar you have to manually add events to.