"beamer can export to PDF or PS", beamer doesn't export anything. It is a LaTeX class and LaTeX compiles the document to PDF (pdflatex) or DVI (latex) which then is mostly converted to PS. There is of course no powerpointlatex, so you will need to convert the PDF or PS somehow to a format PP can read, which would be RTF (Rich Text Format) or some Windows vector format like EMF or WMF. However, I would do it either with one or the other software. They do not mix well.