auto compress in Access 2000

The simplest way is to use the access command line option /compact
You can get details of this by asking the office assistant for "compact command line".
To run it automatically, you could use a scheduling program such as windows scheduler from the Start button, go to Programs|Accessories|System Tools|Scheduled Tasks and Add Scheduled Task.
You must make sure that the database, or databases, you want to repair/compact are closed before the operation begins because the operation needs exclusive access to succeed.
HTH
John