The location of scanpst depends on the version of your OS, and the version of Office. Scanpst was only included in windows95. If you are running any later OS than that you will have to have office installed on the system to have it installed, so it is not installed by default by the OS.

excerpt from-;en-us;197316

The Inbox Repair Tool ships with Microsoft Windows 95, and is also on both the Microsoft Outlook 98 and Microsoft Office 2000 CD-ROM. It is installed automatically during setup. This utility is also installed with the Windows Messaging Service Setup on the Microsoft Windows 98 CD-ROM. You can find these programs in the following folder:
<CD drive>:\tools\oldwin95\message\us\wms.exe

In Windows 2000, you can locate these programs in the following folder:
<CD drive>:\Program Files\Common Files\System\Mapi\1033\NT\Scanpst.exe