It's actually pretty easy... I had to take mine off and put them back on not too long ago.
You don't have to remove the bumper, and it doesn't make it any easier (at least mine was really easy with it still on). If you're having trouble there, remove that little piece of the sideskirt that's not attached to the rest, all you have to do is take out the bolt and then slide it off toward the wheel.
That's how I did it on my 2000 ZX3 at least... hope it'll work for you.
Exterior Mods: Dents, broken glass, bent axle... oh, not mods 'eh?