I think (and will confirm) that in order to do the Office Web app stuff in SharePoint 2010 foundation you’ll need a license of Office Web apps that (I think) is only via VL. Now mind you once you are in the VL system you can buy single licesnes.
Now what’s the licensing requirements for Office Web apps? Stay tuned.. I’ll research that as well.
Office Web Apps is available to users through Windows Live and to business customers with Microsoft Office 2010 volume licensing and document management solutions that are based on Microsoft SharePoint 2010 Products.