It would be nice if OpenOffice then also knew what to do with the documents, and did so automatically.

I seem to remember a command line version of OpenOffice that did just these format conversions, but I can't find it because it either doesn't exist or I'm missing the appropriate search terms.

Update: Ah hah - you can launch (some versions of) OpenOffice in "headless" mode and then talk to it via Win32::OLE or TCP, at least according to this random Google result. This would be the approach I would pursue.