The Operations Manager 2007 free disk space script monitor had the same problem the original mom 2005 script had. It required a disk to cross both a percent free and free megabytes thresholds before an alert would be fired off. This script only works on logical disks, not mount points. Monitoring of mount points is done by another script/monitor.
This management pack contains one Monitor named Logical Disk Free Space – Customized that runs the modified Operations Manager 2007 free disk space script. The monitor is setup to run every 15 minutes on the hour. The monitor is disabled by default. There are four rules to catch possible errors that are written to the agents Operations Manager event log.