Microsoft has released 2 tools under an open source license. These 2 tools will allow developers to edit an pst-file without the need for Outlook to be installed on a machine or even for the machine to be running Windows.
The tools and their projects are hosted on CodePlex;
Download: PST Data Structure View Tool
Download: PST File Format SDK
View: Microsoft Delivers on Interoperability Principles With Office Outlook
The tools follow the earlier released Outlook Personal Folders File Format (.pst) Structure Specification.