What are the extra icon sets and how could I use them?

The image pack is listed just a little bit below the download, here's a direct link. I haven't downloaded it myself, but I'd say it should auto-detect your OpenOffice.org Portable installation and if not simply set it to X:\PortableApps\OpenOfficePortable (where X: is your drive letter).

Then, open up any OpenOffice.org Portable application and go to Tools from the menu and select Options. Under the expandable "OpenOffice.org" category select "View". There's an "Icon size and style" area in that View settings pane.

Hope that works for ya.