Yes, putting together the parts is rather easy. The key is compatibility. If you buy everything compatible, you'll be fine.
And MOST cases are universal. Your best bet is to get the mobo and the case first, make sure they fit together, and then go from there. Next comes a hardrive, I'd suggest duel, one for the OS and one for files. That's an easy task, as hardrives are universal. Now you want a power supply. Get MORE wattage than you need. I'm currently having power issues and I'm technically budgeted on my power. Now get ram, a soundcard, and a graphics card. All of that should be relativelly strait foreward. Stick with the major companies like kingston etc. By the way: You can never have too many fans. I'm a 3 fan man, but some people like to get by with 2. I live in northern minnesota where 2 is very possible. If you're in a hotter climate, 3 or 4 is my suggestion, but others would argue differently. Monitors and other external devices are pretty easy to shop for. LCD is better for gaming. Wireless optical mice are the wave of the future, you ask me. Wireless keyboards are also handy if you like to move around a lot. Although, some people say wireless isn't good for gaming, I haven't noticed a single bit of downplay in my gaming due to them. Speakers... eh, I prefer a damn good set of headphones, so you can't really ask me anything here. Soundcards... well, people tend to spend way too much on soundcards if you ask me. Then again, sound isn't as important to me as graphics are. It's all dependant on your preferences.
As far as the OS goes, get it off of E-bay for cheap. XP Pro is the only thing I'd personally settle for.
You've got a VERY nice amount of cash at your fingertips. Get what you want more. You don't HAVE to get top of the line if you don't really care about it. That's what's nice about building your own box is that you don't HAVE to have the top of the line everything and pay for it all. You can make comprimises to increase technology with something else.
Good luck, and if you give me any specifications on what you'll be doing with the machine, Gaming, what types of games, video editing, etc, I can help you choose parts. PM me on AIM xone009 and I can walk you through it, even. Although, Yoshi is probably far more experienced than I am. I have a few bias' because of my lack of experience, as well. Some people hate kingston memory, but every stick I've had, which is 3, hasn't ever given me issues.
JediKirby
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