i did this exact same thing 8 months ago on my r33 s2 gts-t.
Basically the easiest way i found after swearing for agood 2 hours why the basterds wouldnt come off was the following
Put the screws into the holes, instead of pulling like i did just keep screwing them in till they get really firm as they will act as leverage to push the rotor away from the back. Get a rubber mallet and give it a whack (not to hard obviously) working around the corners. It should pop off if it doesnt keep trying to turn the bolts as they are the key when they have managed to loosen the rotor off a little bit they will come off easy as
Cheers Leigh