Not possible. Outlook Express does not use and cannot create a PST file.
Only Outlook does.
Just open the file in Outlook using File > Open > Outlook Data File, and
copy what you need from it.

Signature
Russ Valentine
[MVP-Outlook]
>I have an Outloook Express ".pst" address book file from my previous
> employer. I don't want to have to type in all of the contacts from this
> previous version of Outlook now that I am using Outlook 2003. How do I
> copy/import the information from the "old" Outlook to the "new" Outlook?
> Thank you!!!