I'm a mac programmer (among other operating systems), but there's an easier solution. Go to the "Personal Message Options" in your account and set "Notify by email every time you receive a personal message:" to Always. Then you can set a rule in Mail.app to run when it notices these emails and run an applescript to notify you as loud or obtrusive as you like. Or you can just check your email.
And this thread should probably be moved to "Forum Discussion".
Joseph Elwell.