hi,
here is how you can create an entry in a .plist file:
set nameOfEntry to "InstallDir"
set value to "Applications:applicatinFolderName" as text
set PlistFile to "/Library/Preferences/com.plistnameWithoutExtension" as text
do shell script "defaults write " & PlistFile & " nameOfEntry " & value
as i could not find any infrormation, i hope it helps others.
cheers