Digital Media is all the rage in Marketing/Advertising these days (just think about how much motion graphics,animation,flash and video content has increased on tv and the internet in the last few years) so you wont have much trouble getting work...
You wouldn't need a post-grad business qualification in this field unless you wanted to get into the management side of things (...and even so pure experience will help you more for that), what employers want is to see an amazing portfolio of work that shows them you have the ability to do great things...