By default, Windows NT posts an alert when the amount of free space remaining on your disk falls below 10 percent. With a 9Gig HD, you still have 900Meg available. To alter this behavior, edit:
Add Value DiskSpaceThreshold with a type of REG_DWORD and set it to the percentage of free disk space remaining before an alert is sent. The allowable range is 0 - 99 percent.