Well, I just spent the better part of 4 hours changing the plugs and wires in my buddy's '98 Sport. Plugs and wires were probably in for well over 100k miles. NO IMPACT WRENCH NEEDED! Lotsa swear words and some serious muscle to get 'em out because they were in really tight, but we got it done Needed to use the breaker bar on several, but they all came out. Middle plug on the passenger's side was by far the worst. Ended up pulling the tranny dipstick tube loose, the air filter and the filter base tray out to get access. Rear plug on passenger's side is easy if you crawl under the vehicle and go up between the frame rail and the splash guard.
Pensa, you're right...anti-sieze on ANY threaded object (excluding head bolts) going into an aluminum component.
Brooklyn, trying to drive the plug in to break it free will most likely shear it off or strip the head. Plugs are design to seal when properly torqued, and with an aluminum head, you're just asking for trouble. Wait 'till the motor is cold so that you don't have an expansion problem, and ease 'em out with a breaker bar if necessary. Besides..you ain't gonna get an impact wrench to where most of the passenger's side plugs are. VERY short extensions and wobble head ratchets are the trick.