Here's the actual code I'm using
#Instantiate the PowerPoint component.
$ppoint = new COM("PowerPoint.application") or die("Unable to instantiate PowerPoint");
#Show powerpoint
$ppoint->Visible = 1;
#Create a new presentation
$ppoint->Presentations->Add() or die ("Could not create presentation");
//Add a slide to the document
$firstslide=$ppoint->Presentations[1]->Slides->Add(1,1);
//Save the presentation
$ppoint->Presentations[1]->SaveAs("/path/test.ppt");
$ppoint->Presentations[1]->Close();