Office 2003 PIA:
RegKeyExists(HKLM, 'Software\Classes\Installer\Features\9040941900063D11C8EF10054038389C')
Office 2007 PIA:
RegKeyExists(HKLM, 'Software\Classes\Installer\Features\00002105501100000000000000F01FEC')
Office 2010 PIA
RegKeyExists(HKLM, 'SOFTWARE\Classes\Installer\Features\00004109501100000000000000F01FEC')