Outlook Express (and Windows Mail in Vista) do not support .PST files from Outlook. You can however, import both mail and contacts from Outlook if Outlook express is running on the same PC as Outlook.
Here are some instructions on how to import and export data in Outlook Express: http://support.microsoft.com/kb/270670
Class: Information Worker: Outlook 2007 Power User*
Date: November 12, 2008
Location: Indiana State University
*The Information Worker series is available through LanTech Training in Indianapolis. Please visit their website for more information