Scanpst is found in your Office installation folders, usually C:\Program Files\Microsoft Office\OfficeXX, where XX is your version of Office.
Replace XX in the following to match your version, then copy and paste it into the Address bar of Windows Explorer and press enter to open ScanPST. (Outlook 2007 = 12; 2003 = 11; 2002 = 10; 2000 = 9. If you are unsure of your version Help, About will list the version in '12.6310.5000' format. If Outlook was installed as part of a suite, Help, About in any of the Office programs will have the correct version number.)
After scanpst opens, click Browse and browse to the location of the PST. Or paste the following line in the File name field and click Open. This will open the PST location in the file browser. (This path works in all versions of Windows if Outlook created the pst. If you moved the pst, you'll need to click Browse.)
Select your PST from the list (most people will have just one) click Open, then Start to begin testing the PST
When ScanPST is finished running the tests, a dialog reports the errors found. If you need to repair the PST, always make a backup.
See the following pages for more information: