Can I open a saved .pst file (on disc) in Outlook Express 6 when the email saved were in Outlook 2007?

I was working on Outlook 2007 and made a back up (on disc) of my emails in .pst format. I am currently working on Outlook Express 6 and really need to view some of those saved emails. Is it possible to open these emails to view? My system says it cant open the .pst file when I click on it in the disc drive. Any thoughts gratefully received.
Can I open a saved .pst file (on disc) in Outlook Express 6 when the email saved were in Outlook 2007?
Unfortunately, that may not be possible. Reading "newer" protocols with an "older" program generally is not possible due to updates to the programming. 7 might open 6, but 6 probably will not open 7.