I think one of the bigger arguments for Mac are Final Cut Pro and Shake, which you can use to edit and composite your movie. Both are Apple-only products and have become industry standards in a very short span of time.
On the other hand, one of the bigger arguments for PC is that they're way cheaper and while the software may not be as good, it's still much more than adequate for what you want to do, certainly as a beginner.
So, get what you can afford and are more comfortable using. I don't think you're going to suffer by picking either one at this point.