If you can work on a messed up cocker you can build a computer with a blind fold on. The other posters here have given you really good advice on what to buy and where to shop.
I have built many computers from scratch and the key is to get all the correct parts that are compatible with one another. Look around at all the web sites that are listed and feel free to pm me with any questions about will this work with this etc.... Also, for video gamers, amd systems tend to give you more bang for the buck than intel (it is a whole hardware design thing that you will not be interested in).
Edit** I answered this post on a computer that I built last year for 200 dollars running
Gentoo Linux as the OS. I believe that will qualify myself as a true computer geek.