Using Try Catch Blocks In Stored Procedure

The following two stored procedures works fine. I need to add try catch blocks in the stored procedures. How to do it? Pls modify my stored procedure with try and catch blocks and in the catch block i need to call the Procedure called ErrorMsg which contains error severity.

Procedure 1
------------
set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
go

-- =============================================
-- Author:  C.R.P. RAJAN
-- Create date: March 26, 2008
-- Description: PROCEDURE FOR IMPLEMENTING SOFT PURGE
-- =============================================
ALTER PROCEDURE [dbo].[SP_SOFTPURGE]
@POID INT
AS
BEGIN
UPDATE POMASTER SET FLAG=1 WHERE POID=@POID
SELECT * FROM POMASTER WHERE FLAG=0
END

Procedure 2
-----------
set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
go

-- =============================================
-- Author: C.R.P. RAJAN
-- Create date: March 26, 2008
-- Description: Stored Procedure for Hard Purge
-- =============================================
ALTER PROCEDURE [dbo].[SP_HARDPURGE]
 @PoId INT
AS

BEGIN TRAN
 INSERT INTO ARCHIVE SELECT * FROM POMASTER WHERE POID = @POID
   IF @@ERROR != 0
   BEGIN
      ROLLBACK TRAN
      RETURN
   END

   DELETE FROM POMASTER WHERE POID = @POID
   IF @@ERROR != 0
   BEGIN
      ROLLBACK TRAN
      RETURN
   END
COMMIT TRAN
SELECT * FROM POMASTER