PPT has a proprietary format which is unknown to the Web. I would suggest you parse the file on server side, map it to some HTML which you will need to compose on the fly, and present it to the user in your HTTP response.
To work with PPT, you would need to use MS Office Interop: http://msdn.microsoft.com/en-us/library/microsoft.office.interop.powerpoint
You can reference appropriate assembly if the Office is installed on the server side. The assembly will be installed in the GAC, so you would reference it from the tab ".NET" of the "Add Reference" window.