tune stored procedure to reduce deadlocks

Hi can anyone give me some tips on how to tune the following stored procedure as its giving me deadlocks?

CREATE PROCEDURE Check_CaseLockMessages



@UserId as int,
@Type as tinyint
AS
/*
Created By:      Chris Kerrison
Date Created:      30 Apr 2001
Purpose:      determines whether a message should be send to a user relating to a case.  The Store Proc works in two 2 ways:
            1) To identify if any other users are requesting a case opened by the User Id passed in
            2) To identify to a user that a Case they have request has been released by another user
*/



if @type = 2
   BEGIN

      Select       csCaseID,
            FirstName + ' ' + Surname as UserName
      From         CSCaseLock a with (nolock), HRHumanResources b
      where       a.LockType = 2
      and      a.UserId = b.HRHumanResourceID
      and       a.LockingUserId = @UserID
      and       a.FlaggedToUser = 0
      order by csCaseID
      -- Update these records so that a message doesn't get sent again
      Set NoCount On
      BEGIN TRANSACTION
      Update       CSCaseLock
      Set       FlaggedToUser = 1
      Where        LockType = 2
      and      LockingUserId = @UserID
      COMMIT TRANSACTION
      Set NoCount Off
  END
ELSE
   BEGIN
      Select       csCaseID,
            FirstName + ' ' + Surname as UserName
      From         CSCaseLock a with (nolock), HRHumanResources b
      where       a.UserId = b.HRHumanResourceID
      and      a.LockType = 3
      and       a.UserID = @UserId
      Order by CSCaseID
   END
GO

Cheers