How to open ODP files on Windows XP without having OpenOffice installed

"conversion always bears the risk of loosing font and text formatting, get OpenOffice Portable. it's free and can be used from a USB stick and doesn't have to be installed.

open the document in OpenOffice and save it in a format compatible with your word processor."

You may be able to use this to let MS Office convert them, or an online service like media-convert to transform it into a more usable file format.