What versions can I have for setting up SQL Server Transactional replication Can anybody help me knowing what versions can I have replication for Publisher , Subscriber and Distributor. 
Do I need to have all 3 servers as same sql server version or can I mix the versions ? what are Limitations if I have lower and higher versions and what are the recommendations?

Question 1 :
What possible SQL Versions can I have for Publisher   ?
What possible SQL Versions can I have for Subscriber  ?
What possible SQL Versions can I have for Distributor ?

Question 2:
Also, is there can I have mix of Enterprise and Standard and Express Editions for Publisher, Subscriber and Distributor?

Thanks in advance.
Yes, you can have several versions of SQL Server involved in a replication set up.  You are limited (generally speaking) to the least common denominator of functuality.  That may be just fine for you, but it is something to consider.

SQL Server 2xxx Express can only be a subscriber in a replication landscape. So as long as data only needs to move to the Express database you can use replication.

Microsoft has documented this for SQL Server 2008 R2 at: http://msdn.microsoft.com/en-us/library/ms143241(v=sql.105).aspx