Yeah, Ovi installs come through App manager, as do ALL installs unless you go through x-term.

Try visiting a site that offers downloads for the N900, using your N900. Here's an example Rightware Kanzi UI and download the N900 demo.

Your N900 will tell you that you need to add the Rightware site to the repositories, which it will do if you allow it to do so. Then it will download and install via App manager.