Originally posted by Savaric
Motherboard will probably take a lot of consideration.
Well, obviously it has to match your CPU. Beyond that... it really depends on what you want to stick in this computer. If you're putting in a hot graphics card, for instance, you don't need much from the onboard. You'll probably get 100Mb ethernet, but if gigabit is of value to you, shop around and you'll probably find a mobo that provides all you want. Etcetera.

Exception being the case. How do you pick a good case? I don't care about flashy neon lights or cool looks. Good ventilation and room for components is what I want.
Measure the space on your desk, subtract a bit to allow for cables, and then get the biggest case that will fit. Although - Having found specs for a case that appears to fit, it might be worth knocking up a carboard mockup - cut down a box to the precise size of your proposed case, and physically place it on the desk, to see how well it'll all fit together.

I don't know if you have any way to know these things before you buy, but the ideal case is easy to open, close, and move components around in. It needs to have enough structure to withstand the rigorous stresses it'll get in everyday use, but not so much structure that it gets away from you.

Do you need front panel facilities? For example, USB ports, headphones jack, etc? You often need to match these across mobo and case. It can be quite handy, if you need it, but if it's not provided, tough.

What's the shape of the power switch? Is it convenient, without being accidentally pushable? Does the box orient itself in a convenient way? All fairly minor questions, really.

Will I need an extra fan in this thing or is the cpu cooler and psu fan adequate? No overclocking on this.
You're looking at putting in a hefty video card. You might need some extra cooling. As I'm not one to do that sort of thing, I really don't know... someone else will answer this part.