I want to build a desktop computer with my 11 year old son to play
computer games on.  A kit would be best.  The ideal result would work,
look cool, and be faster than his friend's computers.

And your question is what?

Are looking for how and what parts?  Try this tutorial...http://www.mysuperpc.com/

If you are looking for a kit, Tigerdirect.com has the best one's. 
They sell a wide variety of barebone kits.  My friends and I have
bought a couple kits from Tigerdirect.

The main page for Tigerdirect's barebone kits:

http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=2251696&Sku=A455-2112%20F

If you don't know what you're looking for, or are looking for
suggestions, I recommend the following kits.  Not only will they look
cool, but they will be great for games.  All that you will need to do
is buy a couple of seperate parts, such as a graphics card,
speakers...etc.
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This 1st kit is very fast and fairly cheap.  Not to mention it has a
pci express slot so it can use the newest and best kind of graphics
cards.

http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=2120037&Sku=A455-2116%20A
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Another great kit that looks cool but doesn't come with as many
components would be this:

http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=2251696&CatId=332
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Now for graphics cards and everything else, I recommend Newegg.com

For a cheaper graphics card that can run almost every game at max settings:
http://www.newegg.com/Product/Product.asp?Item=N82E16814150130

For a more expensive graphics card that kicks ass and comes with Quake 4:
http://www.newegg.com/Product/Product.asp?Item=N82E16814125031

I hope this info will help you and your son out.

thanks very much canadianhelper!