Adding New Columns To All Tables Using A Script

Hi, I'm trying to add a modified datetime and userid to all 72 tables in my
SQL 2000 database. I have the script to do one table, and a cursor, but it
won't run across all tables. Any help would be appreciated. Thanks...

DECLARE @tName varchar(40)
DECLARE C1 CURSOR FOR
select name from sysobjects where type = 'U'
OPEN C1
FETCH NEXT FROM C1 INTO @tName
-- Check @@FETCH_STATUS to see if there are any more rows to fetch
WHILE @@FETCH_STATUS = 0
BEGIN
-- This is executed as long as the previous fetch succeeds
BEGIN TRANSACTION
SET QUOTED_IDENTIFIER ON
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
SET ARITHABORT ON
SET NUMERIC_ROUNDABORT OFF
SET CONCAT_NULL_YIELDS_NULL ON
SET ANSI_NULLS ON
SET ANSI_PADDING ON
SET ANSI_WARNINGS ON
COMMIT
BEGIN TRANSACTION
ALTER TABLE @tName ADD
ModifiedDT datetime NULL,
ModifiedUserID int NULL
GO
COMMIT
FETCH NEXT FROM C1
END
CLOSE C1
DEALLOCATE C1
GO