Any PST file's path can be hacked from the store's EntryID. See http://www.outlookcode.com/codedetail.aspx?id=680 for sample code.
The default AutoArchive file is stored in the Windows registry as part of the mail profile. The KB article at http://support.microsoft.com/default.aspx?scid=kb;en-us;836755 provides the clues needed to find it (assuming you know how to read PRF files).

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Sue Mosher, Outlook MVP
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Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
> Hi all,
>
[quoted text clipped - 9 lines]
> Thanks alot --
> Markus