http://msmvps.com/blogs/bradley/archive/2006/05/25/97044.aspx
First the caveat.. the SBSmonitoring database shouldn’t be that big.. if it is …. your monitoring program isn’t running properly and purging the database as it should so rerunning the monitoring wizard is probably the best plan of action… but if you need to clean up that monitoring file… here’s some info from the newsgroups…
1> We can simple rerun the Monitoring wizard to purge the
SBSmonitoring.mdf database.
NOTE: After doing the following steps, the original performance and usage
data will be removed. The server will start to collect new counter value
from the beginning.
1. Open Server Management console, navigate to 'Monitoring and Reporting'
snap-in. In the right panel, click 'Set Up Monitoring Reports and Alerts'.
2. In the wizard, click 'Next'->Select 'Reinstall monitoring
features'->Select the options if you want to receive the report e-mails.
Check 'View the usage report in Server Management' option. If you want to
receive the usage report e-mail, also check the option below->Add the users
which you allow them to view the usage report to the authorized
list->Select the option if you want to receive the performance
alerts->Click 'Finish' button to complete the configurations.
3. After doing the above steps, the performance and usage data will be
reset. Please wait for 24 hours and then you will see the reports through
the Monitoring and Reporting console.
2> If you are using SBS Premium and have SQL server installed:
You can use the SQL Client Utilities to try and shrink the database. In
SBS, there is a job SBS_Database_Cleanup that is scheduled to run at 3:00
AM everyday, to delete over 90 day old information from the monitoring
database.
You can manually run the SBS_Database_Cleanup job, and use DBCC
SHRINKDATABASE, DBCC SHRINKFILE or use Enterprise Manager
to reduce the size of the database.
3> If you are running SBS Standard:
You need to use osql to connect to the WMSDE instance, and use transact SQL
commands manually to request the database be shrunk ("dbcc shrinkdatabase(
SBSMonitoring, <% free space target>)").
4> If you need more space on your C drive, I would also suggest moving
available data from your C drive to other partition on your Server. The
following white paper demonstrates this scenario in detail.
Please refer to Step 5: Move the Monitoring Database in the following white
paper.
Moving Data Folders for Windows Small Business Server 2003
http://www.microsoft.com/technet/prodtechnol/sbs/2003/maintain/movedata.mspx