I had the Apache server.xml set up correctly, as I've done countless times... but the default document wasn't working... and all non .cfm files were pointing to IIS's default site.
Turns out, I hadn't made a website entry in IIS, to parallel the configuration in Apache's server.xml entry.... Its all making sense now. Requests routed to apache knew where they were because of server.xml, but IIS had to have a configuration to set the webroot for all the other file types (such as .html, .css, and .jpeg)
I still can't figure out how to make a site in IIS that isn't inside C:\inetpub\wwwroot\ as the permissions get all screwy... I'll leave that for another day.