The Platform Installer UI is not as intuitive as I would like, there is a menu that doesn't really look like a menu, by default "Spotlight" is selected and we are not listed there, but if you click "Applications" we should be listed there.
However, the version of mojoPortal currently in the Web App Gallery is not the new release. To get the new release you can use our custom feed for Platform Installer.
Also you posted this in the developer forum, the platform installer only installs the pre-compiled version of mojoPortal not the source code, to get the source code you need TortoiseHG.
Hope that helps,
Joe