Web Analytics database uses the table partitions features from SQL 2008

In SharePoint 2010, the only configuration that you can do is the retation policy on the Web Analytics Service applicaiton:

1. Click on the Manage Service Applications
2. Select the Web Analytics Service Application that is linked to the database.
3. Click Properties
4. Change the Data Retation Period

In SQL 2008 you can schedule to shrink the files and released unused space. Using the SQL agent, I would not recommed doing this for production enviroments as it can affect the performance of the Web Analytics reports.