You can't create triggers on system tables in SQL Server 2000, although this
functionality will be available in the next version of SQL server.
What you need is a proper development process where developers check their
changes into a source control system, and the database is build on a regular
basis from the source. If you can't achieve that because management won't
allow that, as it looks like in your case, I would advise you to buy SQL
Compare from www.red-gate.com, and schedule that at night to make snapshots
of your database so you can compare it from day to ...