I am thinking about trying to build my own PC. I used to have a link to a website that you could buy every thing you needed from and when you picked one item it would only show you COMPATIBLE items so that every thing worked together. In other words you wouldn't buy a mother board that was too big for the case you wanted and you would get the correct type of RAM to fit in the mother board. This site also had comp building tutorials for those of us interested in learing how to do this sort of thing.

I am not wanting any thing special as it will just be my children using it if I can actually get it to work. They have several childrens GAMES that they currently play and like to use paint to draw. So there is no need in a powerful video card or processor. I am also not looking to spend alot of money.

Any advice and/or U.S. websites would be greatly appreciated.

ThanksNewegg.com is surely one of the top online sellers in the U.S. I can't say that they do what you want regarding compatibility but they have a list of helpful links at http://www.newegg.com/Info/KnowledgeBase.aspx. And, indeed, they do organize their product listings to help you focus your search. For example, if looking at motherboards, you can select AMD-compatible Motherboards or Intel-compatible Motherboards.

Another big online seller is tigerdirect.com. I'm not aware of any online sellers that provide the detailed compatibility info you seem to have in mind. Perhaps you should look at the "barebones" packages. They are basically partial systems, and then you buy the remaining components.

I have a feeling you're overly concerned about compatibility. Keep in mind that any of the major brands of hard drives and CD and/or DVD drives are compatible with PRACTICALLY all modern motherboards. When shopping for memory, take a look at crucial.com or kingston.com and use their memory selector tools to help select the right memory.
Try http://www.tigerdirect.com/ I have only ordered a couple of things from there but they both work fine. They have a huge selection on everything computer!