Barebone systems are not usually a good thing to get because (usually), they try to put lower end parts into them...unless you order it directly from a dealer/shop that lets you tell them exactly what to put in it...
But then, if you're going to do that, you might as well tell them to build you the whole computer.
www.monarchcomputer.com builds both computers and barebones and you can customize everything that goes into the computer, from the PSU to the CPU (brand name, model number, etc)
....but make sure you read some guides or know what you're doing before customizing....(if you don't want to do lots of research, you could take the quick route and read some system buying guides on
www.anandtech.com)
Brand names don't matter when it comes to who builds the system. HOWEVER, brand names *do* matter when it comes to the parts that are *inside* your system. Generic hardware is *never* good. And I would only buy a computer from builders that I've heard good things about (and those with good resellerratings)...and if it's a brand you've never heard about, you need to make sure that they're not cutting corners.
Nothing, really, that you should be aware of. I'd avoid hp, compaq, gateway and the like. Dell is okay for your uses. Big hard drive and 512 ram are good for video editing.
Like I said, monarchcomputer.com is supposed to be good. I've heard good things about abscomputers.com as well.
Good luck.
*edit*
Rubicon said "never use windows". I'd have to disagree. If you ever do any type of gaming, it's a pain in the ass to have to run a windows emulator to play them. Windows is a very commonly used OS. The interface is user-friendly. Other people will be familiar with the interface so, if you have a problem it will be easier to get help. Unless you have a real reason not to use windows, I'd say windows is fine.
BTW, I'm not saying this because I'm a huge windows fan. Personally, if I wasn't a gamer, I might use linux. But I always reccomend the popular program to those who aren't aren't hardcore about their computers or who aren't very computer savvy.