How to purge System Restore in Windows Vista.
Note: This will delete any previously created restore points.
What to do
- Go to Start|Control Panel|Backup and Restore Center.
- On the left, select 'Create a restore point or change settings'.
- In the window that opens, select the 'System Protection' tab.
- Each available disk which is listed, has a checkbox alongside it. Deselect each of these checkboxes.
- A new window is displayed, select 'Turn System Restore Off'.
This disables System Restore. You should then immediately re-enable it.
- Reselect all the listed drives.
- Click 'OK'.
- Restart the computer.
Another knowledgebase article describes how to purge system restore in Windows XP.