As many others have done, I bought a small SPST switch and mounted to the very top of my cabinet after drilling a small 1/2" or 3/4" hole so I can stick a finger into that hole and press the button. Just like the power button on your computer, it simply turns on the computer when pressed. At the other end, I just used the PWR connector going into the motherboard and the computer p/s itself is plugged into the CONTROL plug on my Smart Power strip so it has constant power. The marquee light, monitor, fans, and speaker amplifier are all plugged into the ACTIVE outlets so once the computer turns on, everything else in the cab turns on.
Right now, because I'm still working on the software side, I haven't figured out an easy way to get the cabinet to turn off -- what ends up happening is I use the actual keyboard that I still have plugged in vis USB to tell Windows XP to shut down. Once the computer shuts off, the Smart Power strip turns off everything else. I need to figure out how to get that to happen using just the cabinet controls.
Good thread...I'll keep an eye on things to see if there's a surefire way to make this work.