Nope. You can only use software designed for CE.
Certicom is now listing WM2003 on their compatibility list for MovianVPN.
Click Here For Link. Scroll to the bottom of the page, and it now lists PocketPC 2003 (aka WM2003) on their system requirements.
I have not tried it yet on WM2003, so you might want to check out a demo of it before buying it.