There are a couple options...
Option 1. Hack a relay into a Power Strip, (there are plans on the Net for this option). Basically, the computer is in the only "always on" plug, and when the computer is turned on, the relay is activated, turning on the rest of the equipment.
Option 2. If you are using an AT Power Supply, you can simply use one of those power strips, and relocate the switch from the power strip to somewhere on the cab.
Option 3. If you have an ATX Powersupply and can find a power + momentary switch, you can wire the on button to that switch, along with the power strip. I.E. you would flick the switch, everything would power up except the computer, and then you press the switch a little farther and the computer cuts on too.
Option 4. Run the power switch to one of your arcade buttons, and just use the two button method, one for the computer, and one for everything else.
Personally, I would use Option 1.... but thats just me.