Microsoft provides the Inbox Repair Tool for correcting most problems with damaged Personal Folders .pst files. If you do not see the Inbox Repair Tool on the Start menu, under Programs | Accessories | System Tools, use Start | Find or Start | Search (depending on your operating system) to search your system for Scanpst.exe.You will need to know the location of the .pst file that you want to repair. See Outlook & Exchange/Windows Messaging Backup and Dual-Boot for information on file locations and ways to determine the location of a .pst file that you can see in Outlook.
Usage | Notes | Other Tools | More Information
Usage When you run Scanpst.exe, it performs a number of tests. If it finds errors, it asks whether you want to make a backup copy of the original file (always say Yes), then tries to correct the errors.
If you run Scanpst.exe against a .pst file that Outlook 2003 created for a local copy of Windows SharePoint Services events and contacts lists, you will get an error message that you can ignore. See You Receive an Error Message When You Use the Inbox Repair Tool to Scan a .pst File
For seriously corrupted PST files, try running Scandisk.exe (look under Programs | Accessories | System Tools) first, then Scanpst.exe, repeating 3-4 times until neither program returns an error. We’ve know this technique to restore data that the user though was lost forever. And if that doesn’t do it, you can try our tips to repair a 2gb Personal Folders file or Offline Folders in Microsoft Outlook.
If the file is on an NTFS volume, you can’t use Scandisk.exe so easily. One approach, for Windows 2000, is to open the drive in My Computer and use the Tools menu commands to scan the disk. You may need to restart Windows for the scan to run.
Notes You can use Scanpst.exe not only on PST files, but also on offline folder .ost files used for offline access to Exchange Server folders. If an OST file is corrupted beyond the ability of Scanpst.exe to repair it, you will need to change the settings for the Exchange Server service (Tools | Services) to use a new OST file, then synchronize it with the server.
There may be cases where you need to run both ScanPST and PST2GB. See OL2000 Error Message When You Start Outlook 2000 or Try to Open a Personal Folders File.
Another approach is to use a hex editor remove a single byte from the middle of the PST file, then run Scanpst. A hex editor is a tool for editing raw files; every Windows shareware site has several to choose from. Eugene McCarthy of FAO Headquarters in Rome recommends the free iHex editor, which loads only 64kb of the file at a time, making it ideal for tinkering with extremely large PST files. For simple Scanpst repairs, Eugene recommends changing the first byte of the PST file from hex 21 to 00.
There is no comparable program for cleaning up corrupted Personal Address Book (.pab) files. You may be able to view and recover PAB data by opening the file with a hex editor.
More info Source:http://www.slipstick.com/problems/scanpst.htm