SELECT / CASE would be a good choice here. Something like:
 Code:
Select
 Case ExistKey("HKLM\first key...")
  ; ok - do nothing
 Case ExistKey("HKLM\second key...")
  ; ok - do nothing again (an again.. as needed)
 Case 1
  ; No required keys were found - do something, install something!
  Shell "%COMSPEC% /c D:\some\app\install.exe /silent /successful"
  ; check for errors {won't be any, chose the successful install option ;)}

EndSelect


Glenn
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Actually I am a Rocket Scientist! \:D