[Zoolok]

OK, I've just tried exporting an OG file as a vector eps and importing it into ppt. No problems - or at least not when scaling it up 200% or so - no jaggies here (this was tested in OGPro and PPT2k4 using a greyscale image made from "radial filled" circles).

What versions of OG and PPT are you using?
What are you exporting as?