So many replies since Christophe's its old news now but I think:

Code:
 
run '%comspec% /c start "'+ $pptfile +'"'


... will open a command window because the Start command wants to interpret the string in the first set of quotes it finds as a title. The following will work:

Code:
 
run '%comspec% /c start '+'"Some PPT Show" '+'"'+$pptfile+'"'


mole
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mole

Who is John Galt?