If you want one for video editing, get a video editing program. I think all the main ones come out on both Mac and PC. In my opinion, Mac's iMovie is better than Window's Movie Maker. But if you're buying a whole new PC just for that. Then it would be cheaper to just buy a program. Depending on how powerful your current pc/laptop is.
The difference between Mac and PC. Hmmm. I don't think you're going to find a straight answer to that. For one, there isn't really a difference. They do pretty much the same thing. Mac is more expensive. But, some people (like myself) do prefer the operating system over Windows. If you know how to drag n drop, you will be able to use a Mac. Everything is, you could say, simplified. That's not to say there isn't a learning curve though. Some of the language is different. You will come across compatibility issues with Mac on certain programs. BUT this can be countered by the fact that you can legally (and is encouraged) duel boot between Mac and Windows 7.
So if you can afford it. Buy yourself a toy, you will be impressed with Mac I bet. Dual boot it with Windows. You have the best of both worlds then.