How can we avoid having the same case opened by more than one user

Currently by using CRM 2011 for tracking all of our phone tech cases. We have been experiencing some problems when two users have the same case file opened simultaneously.  

When the case is opened by both uses they cannot see any active changes being made.  Who saves last overwrites the work saved by the user who saved first.  This has been a problem when additional notes are added by a user and saved and the second user writes their own and saves completely overwriting any work done by the original.  Is there a way around this?  

Is it possible to:

1.  Alert a user that the case is opened elsewhere

2.  Lock a case that is opened elsewhere

3.  See active changes being made by another user.

4.  Show a list of other uses currently accessing that case.