I'm going to have to say that no, your computer is not protected in the way you would want it to be. The GFCI is for YOUR protection. This prevents you from getting the begeebers shocked out of you. This does not protect your computer from surges, spikes, transients and other garbage on your electrical lines. Devices such as surge protectors operate by diverting the harmful garbage to the ground (most commonly by means of MOVs) so that it does not reach the computers power supply and toast it. If you do not have a ground then there is nowhere to shunt this to and it gets passed through your power supply. Alot of this garbage is converted to heat in your ps which can tax your cooling, and some can be passed on to the sensitive electronics in the computer. Running an extension cord is an iffy prospect unless this is a temporary location for the computer or unless the cord is a short one. It would be too prone to damage.