If you are sure that what you are dealing with is a presentation then try changing the file extension to .ppt in order to open it. You may lose some formatting, and it has mixed results with Office '07, but it is worth a try. Just be aware that if it does not work then you should trash the file and re-download it. Or, with foresight, you could copy the original and make the extension change on the copy- so you don't need to ask for it to be sent back.
OpenOffice Documents Can Be Saved As The Following File Types
- OpenOffice.org 1.x Presentation (.sxi)
- OpenOffice.org 1.x Presentation Template (.sti)
- Microsoft PowerPoint 97/2000/XP (.ppt and .pps)
- Microsoft PowerPoint 97/2000/XP Template (.pot)
- StarDraw, StarImpress (.sda, .sdd, and .vor)
- Unified Office Format presentation (.uop)
Do not try to save an OpenOffice document to any other formats, or the results will be useless.