I built my own a couple of months ago. I gutted my single core and put in a quad Phenon 9950, same as the q6700 but a hundred + cheeper. New PSU OCZ X-stream 600w asus MB, 8Gb ram and a cheep nvidia 8500gt( works fine with all my cg software). I had an extra seagate 500Gb drive already for it. Used the old DVD/cd drives and just replaced the IDE ribions with the IDE round cables for air flow. The case is slightly bigger than normal, older case.

I had so much fun putting it together, that when I was looking for something in the basement, I found my first computer. IBM. The MB fried but PSU was good. So, I dropped the single core I had just replaced into that case. I lucked out with the MB was a mini atx so it fit in the IBM case. I use this for the net and DL's  so I don't have to have any antivirus or firewalls interfering with my other two work stations.

Which my other dualcore is an HP referbished and has been running great for over 2 years. That's another option, check referbished PC's.

Building your own is not for everyone, I did it because I've always been good at building things. Others, it's better to buy and have someone else do it.

The only things I need now for awhile is a new case, full tower, when I find the right price, no hurry, and another monitor as I have an extra PC I never planned for. LOL.