You can and should run the Document Converter (File > Wizards > Document Converter) to convert all those lovely Microsoft Office templates you want to use in OpenOffice. The wizard creates converted copies. You then copy those copies to openoffice\share\templates\en-us\ and they show up in all your template windows. (If necessary, restart the program and/or the computer to make them show up.)
All of that works just great with Writer and Calc, and the converter works just fine for everything, including Powerpoint/Impress. Here's a directory of converted copies.
But here's the deal.
The Powerpoint templates each have a different filename, of course. blue, red, bluefancy, etc.
But they all have the same TITLE, the name that appears in the upper left corner when you're looking at the document. So the converted templates end up all having the SAME TITLE.
So that means that when you copy a bunch of templates to the template directory, all with the same TITLE, the organizer gets horribly confused and won't let you get to more than one.
All you need to do is before you convert, right-click on each PowerPoint template in your file manager that you want to convert, and choose Properties. In the Summary tab of that window, in the Title field, type a unique name. Me, I like to copy the file name from the General tab and paste it into the Title field.
(You might want to assign that promising young intern to this task.)