Earlier this week, we released an add-in that can be installed on top of ProjectWise Explorer SS4 to allow for integration with Microsoft Office 64 bit. The add-in can be downloaded through SELECT Downloads by selecting "Bentley ProjectWise" as the Product.
Take a look here for more information:
http://communities.bentley.com/products/projectwise/content_management/f/342986/t/80712.aspx