Grant Anonymous Access users Contribute access to a Subsite list

I have an anonymously accessible single-server Foundation farm built on an external server that uses a handful of local, non-AD server accounts for admin.

For our other, internal SharePoint Server farms (without InfoPath),  I have set up lists which are contributed to via the newform.aspx form page.

I would like to emulate this functionality, but for our Foundation, anonymous external site.

In the list's Permissions, I've added Contribute to the Visitors group's Read access, which did nothing. Anonymous Users is at the top of the list, greyed out and without a checkbox, with View Items permission.

I'm trying to figure out the right approach, or if it's even doable.

Ideas?

Thanks,

Scott