Backup audit database
The technique you are refering to is called Table Partitioning. However, that is not available in SQ Server 2000. To the best of my knowledge, it was introduced in SQL Server 2005:

http://msdn.microsoft.com/en-us/library/ms345146%28v=sql.90%29.aspx

However, you could build similar functionality by means of scripting:

http://msdn.microsoft.com/en-us/library/aa902650%28v=sql.80%29.aspx