Hi, it can be done but Outlook Express cannot import a pure PST file. So you need to open PST in Outlook. Then import to OE.
If you do not have Outlook, use a friend's computer which has both Outlook and Outlook Express. Import PST into Outlook. Then import emails from Outlook to Outlook Express. Copy the entire folder where Outlook Express DBX files lie to your computer. Then import the DBX files.
So in conclusion you will need to export the pst file to a flash drive then import it to a friends PC running outlook and then convert the pst file to Outlook Express http://www.ehow.com/how_5166282_convert-outlook-pst-outlook-express.html