Hi,
Sorry for the slow reply – I have been heads-down on another project (watch my blog tomorrow 🙂
Are you talking about using the C# Open-Xml-Sdk to do this? Or some other API? Are you speaking of modifying an existing presentation, or of creating a new one?
In general, everything you can do in PowerPoint, you can do via Open XML. You can go into a slide, modify elements and attributes as you like, to give it the same appearance / functionality as you could do via PowerPoint.
There is an easy way to research Open XML markup. Please watch the following screen-cast:
How to Research Open XML Markup