This is how you'd do it in VBA. It should be simple enough to adapt to .Net. It's just a matter of setting a few properties before invoking the .Run method.
Sub Example()
With ActivePresentation.SlideShowSettings
' display a range of slides:
.RangeType = ppShowSlideRange
' Start with slide 5
.StartingSlide = 5
' Specify the ending slide or as here,
' have it run to the end of the presentation:
.EndingSlide = ActivePresentation.Slides.Count
' window, not fullscreen/kiosk:
.ShowType = ppShowTypeWindow
' and show it:
.Run
End With
End Sub