Since you post with a VBA tag, here's VBA code that inserts a Chart into PowerPoint. Note that in order to use Excel.Chart or workbook you need a reference to the Excel object model (PIAs) in your solution. Otherwise use the generic object, but then you won't have any Intellisense.
The AddOleObject method is the key for importing something from an OLE Server. Through OLEFormat you get basic information about the object; OLEFormat.Object gives you access to the object, itself. Note that as far as PowerPoint is concerned, this is a Shape object.
Edit: The lines commented out in the code below create a new object and show how to access the underlying Excel objects.
In order to bring in and link to an existing workbook you need to specify the file name (but not the OLE class!) and that it should be linked. Only the "top-most" Sheet in the Workbook will be displayed. Note that the linked object cannot be manipulated like the independent object - the actual file must be opened in Excel. The user can do this by double-clicking the object; code can do it using shp.OLEFormat.DoVerb 1.
Sub InsertExcelChart()
Dim p As Presentation
Dim s As Slide
Dim shp As Shape
Dim wb As Excel.Workbook 'Object
Dim chart As Excel.chart 'object
Set p = ActivePresentation
Set s = p.Slides(1)
Set shp = s.Shapes.AddOLEObject( _
FileName:="C:\Users\Cindy Meister\Documents\SampleChart.xlsx", _
Link:=msoTrue, DisplayAsIcon:=msoFalse)
'Set shp = s.Shapes.AddOLEObject(10, 10, 600, 200, "Excel.Chart")
'Debug.Print shp.OLEFormat.ProgID, shp.OLEFormat.Object.Name
'Set wb = shp.OLEFormat.Object
'Set chart = wb.Charts(1)
'Debug.Print wb.Name
'Debug.Print chart.ChartType
End Sub