You want professional video editing? Then come to the Mac world. Only Macs can run Final Cut Xpress and Final Cut Pro 4.5 (High Definition). And that's of course because they're both made by Apple. From what I know, Final Cut Pro 4 was the best video editor out there, and now that FCP HD is out, well...It seems that Apple is unstoppable in terms of video editing. The only disadvantage to Final Cut Pro is that it has to be bought with several other applications, and as a result it's a bit pricey ($999 US). The other applications are Soundtrack, LiveType, Cinema Tools, and Compressor. I'm not entirely positive what each one of those does, but I'm sure other people here know and could tell you. Here are the requirements for these programs: http://www.apple.com/finalcutpro/specs.html
Also, Apple just came out with a new program that's somehow related to video editing, called Motion. It's graphics design, I believe. Compared to related applications sold by Apple, it's actually not too expensive, although the system requirements are absolutely unbelievable.
As for disadvantages? Well....First let me ask you this Which computer do you have now, and what operating system is it running? What's the processor? What's the hard drive? What's the RAM? etc.
As for MovieMaker? Nope, it's an XP-only application. MovieMaker is like iMovie for Windows, only from what I've heard it's much better (or at least the newest version, MovieMaker 2, is). But that's for HOME video editing. If you want minor **** like that, then maybe XP would be your best choice. But if you want to enter the professional world of video editing, and do films just like the stars, use Final Cut Pro. It smokes the competition (from what I've heard, hehe).