I don't know if the OP is still reading this thread, but . . .
I sort of agree with the people campaigning against DIY rigs. Sort of. I built my last machine(in 2001, I'm on a 4-year upgrade cycle, ha ha) "from scratch" and had all kinds of "fun" installing the motherboard and CPU. Mostly, I was just nervous, but hell I'm no professional tech. Nothing broke, but I'm sure I put too much of that crappy thermal paste that came with the generic heatsink(think it was a Galaxy), and my poor excuse for cable management, along with poor case selection, gave me a system that was running a little too toasty until I took off the sides and front bezel of the case. Goodbye, air flow and dust protection.
What I wound up with was a very functional, loud, and ugly 1.4 ghz Thunderbird dust bunny. By jove, it worked, but it still wasn't pretty, and the case just sucked.
On the flip side, buying "pre-built" systems is bothersome in other ways. You can put a lot of money down on a system and wind up with a case that looks stupid or with a poor selection of components. Every retail outlet seems to want to lock you into a particular selection of hardware.
This time around, I went for a barebones system. I picked one from Mwave.com, but I'm sure there are other firms out there offering good deals on barebones. I got a much nicer case this time, and I got the cpu and motherboard I wanted(well, mostly, I don't think I'd have any business getting the socket 754 DFI). The only disappointing thing was their selection in RAM, but I got lucky, and the DIMM I ordered with the system was quite bad. I'm RMAing it for a refund and buying the RAM I really wanted off Newegg.
The nicest thing about the barebones bit was that the motherboard and CPU were already installed. Those two items are potentially the most sensitive components you can work with when building a PC, particularly if you've got bad hands and little/no working experience. The RAM was also pre-installed, but it was junk, so that was no help. Given the decent design on the case I got, installing the new DVDRW and harddrive was a snap. The case fans, well . . . okay, that took awhile. Bloody stupid fan screws.
In any case, unless you're a goober like me and order perfectly good case fans packaged with perfectly awful fan screws, you can take a lot of time and trouble off your build if you get the motherbuard and cpu pre-installed properly by . . . oh, I don't know, someone who earns a living doing that sort of thing. That still gives you some flexibility when picking your own PSU(you might get one with your case, but those are frequently crappy and should be replaced anyway), harddrives, CD/DVD drives, video card(s), sound card, monitor, and so forth, and so on. All that stuff is pretty easy to install, especially if you get a case that doesn't suck.