Need Help With Raiserror Function In Ado.net Mssql 2000

I have a stored procedure that raises an error just fine, but the problem is when i want to catch that particular error in client code, how do i go able doing so, i want to display a message in a label when that particular error occurs.

right now all i know about the raiserror function is RAISERROR("Message", Severity, Stage) how do i give it number so i can catch it in code?

ALTER Stored Procedure [dbo].[spName]

..............................................
...............................................


IF (@DummySetKey IS NULL)

BEGIN
RAISERROR('Error: This setkey number does not exist as a valid entry.', 11, 1);

SELECT @ErrCode = @@ERROR
END

IF @ErrCode <> 0 GOTO ERROR_HANDLER

ERROR_HANDLER:
ROLLBACK TRANSACTION
RETURN @@ERROR



client code:

Public Function ExecuteNonQuery(byval connstr as string) as boolean

dim conn as new SqlConnection(connstr)
Dim cmd as sqlCommand(spName, conn)
cmd.CommandType = CommandType.StoredProcedure

conn.Open()

try

dim rowsAffected as Integer = cmd.ExecuteNonQuery()

If ex.ErrorCode = 5021 Then
' display in textbox
Else
Throw
End If
Finally
conn.Close()
end try

if rowsAffected > 0 Then
return true
else
return false
end if
End Function