On another note, one thing that could give you an idea of where to start is look at the specs of an actual gaming PC like from Alienware, Dell, or someone else (I like Alienware) and then hit sites like Egghead, Pricewatch, etc for the parts. OEM parts are ok.
Your basics are:
- Motherboard
- CPU
- CPU Fan
- Ram
- Video cards (Double check the slot type, ie., AGP, PCI-E, etc)
- Sound (most motherboards have on board sound)
- Network (most motherboards have on board gigabit adapters)
- Case (with adequate case fans some pulling clean air in, others used for exhaust to push hot air out)
- Power Supply
- Harddrive
- CDROM
- I wouldn't worry about a floppy but they are very cheap you can get one if you feel you need to.
As far as brands, experience and talking with others who have done this is your best source for brand names.
Myself I like Asus motherboards. Motherboards pay close attention to what it has to offer as far as onboard stuff. Some have everything and all you gotta add is Ram, these don't make good gaming rigs as the video usually isn't that great. Intel and AMD based boards are unique so make sure you buy the right motherboard to go with the chip your buying. Also, make sure you buy the right socket type. Same goes with the CPU Fan, get the right fan for the right CPU. If you have a store like Microcenter or Frys they can also help you by explaining more things in detail.
Video cards basically your main concern is the chip type (NVidia/ATI) Make sure when you buy your video card, the type slot (AGP/PCI-E, etc) matches what your motherboard can have. If your looking SLI, make sure the video card AND the motherboard support SLI.
The case needs to be reasonable compared to the size of your system. Fans are pretty generic, power supplies your main concern is watts, 600w is pretty decent.
Don't EVEN try watercooling until your extremely comfortable with building systems as one slip up can ruin everything you've spent your money on.
I have built many systems including watercooled systems. It's not that hard and when your parts arrive in the mail, from the first system I bought until the last one I still get like a little boy on xmas going through the fresh new parts.
Once you get them, it's pretty standard, they only go in one way. Someone listed some steps above.
Take your time, don't rush into it. DO NOT power it on until you put a CPU Fan on the chip or you will hate yourself. It only takes a few secs to burn up a chip.