SQL DB Space Rules
These Rules monitor the amount of used database space in the SQL Server (including both data and transaction log). Optionally, transaction log can be excluded from the metric.
SQL-DMO library must be installed on the monitoring engine. It is generally installed as part of SQL Server client package, but do check sqldmo.dll is in drive:\Program Files\Microsoft SQL Server\80\Tools\Binn
By default, the Rule recalculates the statistics before obtaining the database space usage. Optionally, this recalculation can be skipped thus making faster (but less precise) readings.