Like the modern beep for messages from personal contacts and the oldschool beep for work contacts.
I am using Windows 8.1 and Skype Version 7.29.80.102
I have read that I could run Skype twice with two profiles, but then I'd have to either add the people from the different group again and remove them from my main profile just to get a different beep on IMs or find a way to forward IMs to the second profile for just the specific group of people.