No, Outlook^® Express is a completely different program. The name Outlook^® is the only part which is the same, but Public ShareFolder runs only under Outlook^® starting from Outlook^® 97, because Outlook^® Express is based on other Interfaces. Outlook^® Express used as interface “Simple Mapi” during Public ShareFolder use the “Extended MAPI “interface of Outlook^®. The basic is complete different.

To explain it a little bit less technically:
Outlook^® Express is based on DBX files and Outlook^® is based on PST files. Both files are accessed over different interfaces. We support the interface for Outlook^® PST files, not the interface for DBX files. (Outlook^® developers may forgive us this not a completely correct explanation)