Outlook EXPRESS toolbar

Hai to all,
I need to add a "toolbar" inside "Outlook express" and "Outlook".
This may be somethin like an ADD-IN.
I developed a toolbar ADD-in with "Microsoft Outlook 10.0 Object Library"
using VB 6, but it works only with Outlook...not with Outlook Express. Why??
Please advice me on this.
Is there any other way to develop toolbar for Outlook Express...Like that of
PLAXO-toolbar (www.plaxo.com)

Thank you