Usually located in Start->Programs->Accessories->System Tools called Inbox Repair Tool.
If it's not there, do a search on your c: drive for scanpst.exe and run that. You'll need to know where your .PST file is located first. To find out, go to Start->Settings->Control Panel and double-click the mail icon. Highlight Personal Folders (or the name of your personal folder) and click properties. You'll see the location of your PST in the path: field. if this screen never shows, then perhaps your PST file is severely corrupted and you will have to do a search for *.pst instead.