I have seen this question come up too often – How to convert PPT to Silverlight.? On researching, here are some tools I found:
Save to Silverlight – Powerpoint 2007 Add-in that converts your pptx file into a Silverlight xap file.
Convexion – A promising brand new PowerPoint 2007 plug-in from ElectricRain that enables users to publish their PowerPoint slideshows to the Microsoft Silverlight and WPF formats
PowerPoint to Silverlight Convertor – Free Tool that Converts Static slides.
Another approach is to convert your Powerpoint to XPS and use a XPS Viewer in Silverlight to view the files