In PPT 2003 or earlier, ensure that your macro security is set to "medium"
(go "Tools - Macro - Security" - "Medium"). This will trigger a confirmation
notice whenever something is opened with a VAB code in there and you can
decide whether to run it or not (and detect whether anything is in there at
all).
Not quite sure how you could embed exe's into PPT or (if possible) detect
them - sorry.
I would think that in 2007 VBA codes can only be activated if the document
is saved as a pptm or potm (macro-enabled)? So you should see it by the file
ending (although this is just a guess - there may still be macros in there
but they're not enabled by default).