Microsoft on it's website (linked above)
Manually Purge the Data Store
To completely and immediately remove the infected file or files in the data store, disable and re-enable the System Restore feature.
WARNING: Using the following steps will completely remove all restore points from the data store. Do not use this method if this will cause problems. When you enable the System Restore feature again, the System Restore feature will create a new restore point and then resume monitoring your computer.
1. Click Start, point to Settings, and then click Control Panel.
2. Double-click System, and then click the Performance tab.
3. Click File System, and then click the Troubleshooting tab.
4. Click to select the Disable System Restore check box, click Apply, click to clear the Disable System Restore check box, click Apply, and then click OK.
5. Restart the computer when you are prompted to do so. When the computer restarts, the data store is purged and the System Restore feature begins monitoring the system again.