When opening files on a MAc, you don't have to use applescript, you can use the FS command. The major difference between pc and mac opening files is how you path them. This is what a Mac fs command for opening files looks like.
Fs Command("exec", "Macintosh HD:Folder:File"
You have to start at the macintosh HD if you are going to any folder other than the current folder, and you have to use :'s instead of /'s.