I find it easier just to go to a gateway.com or a dell.com and customize a pre-existing build. You're not really getting the full cutomization you need as far as parts go (ie, getting the motherboard you like--if any, an expanded line of video cards, wireless adapter, etc.), but at least you can choose how fast you want it to be.
It's really neat in regards to the build in wireless adapter in laptops. They're actually an expansion card that connects to the motherboard. I always thought they were integrated into it until I tore up my old laptop.