I like Shawn's COM method myself, actually shows up as a presentation show instead of just opening PowerPoint like the file call method does.

Here is Mart's code a little different, both work well, but Shawn's does it a bit better (imho)
 
Dim $Msg
Run ReadValue('HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\powerpnt.exe','')+' '+
              '\\server01\presentations\WELCOM~1.PPS'
If @ERROR
  $Msg = MessageBox('There was an error running the presentation please contact support','No Presentation',16)
EndIf