OK, you don't actually need the ISC to drive, but you MUST leave it electrically connected! remove all but one screw from the mounting bracket and swivel it out of the way, then drive. The ISC only comes in to operation on startup, to give a solid start, and if you are driving REALLY slowly, say if you were doing 5kmh up a steep driveway at half clutch or something, or parking... it keeps the engine from stalling. if you can keep your foot comfy on the gas pedal then you don't really need it.
If you disconnect the electrical connector however, the ECU wil shit itself. you won't fry it, but because it's not receiving a signal from the ISC, it will do all sorts of funny shit (well, not funny on Burwood Hwy in peak hour...