Try to get as much of the crud out from around the plugs as possible with copmpressed air or maybe a shop vac. Then soak them with some PB Blaster or somethign to try to free up the rust. You REALLY don't want to break one off in the head. Especially those back ones on a V6.
Some people amaze me with how totally ignorant of routine maintenance they are.
When I bought my truck for example. It was 10 years old and had every original piece of the ignition system on it. Luckily the oil and filters were changed somewhat routinely. The ink was so faded on the plugs you almost couldn't read them to see what they were.
