They are on the sides of the heads beneath a plastic shroud, about where they are on many V6's. The back three are very difficult if not impossible to get to. You shouldn't have to change them for 100K miles or more unless they crack or break for some other reason than wear. If the car is running rough it is probably a sensor that has gone out. With the GM electronic ignition systems on these cars, I believe they will fire so long as two electrodes are somewhat near each other, so worn plugs aren't nearly the issue they were years ago.
Try replacing the plugs and wires
I dont remember if I used different rachet swivels or if I took off the valve cover,one of the two try the swivels first
Underneath the coil packs, which are the square black rectangles with the seven bolts holding them down.
Platinum's
134a
Only the Olds Intrigue with the 3.5 L
5 quarts
Under the glove box.
Need clarification on what you are asking.
Dealerships or junkyards.
If it is a 3.5 unhook battery remove coil packs on top of valve covers and unplug, pull boots from plugs remove plugs with spark plug socket. be sure engine is cool set gap is printed on emision tag. make sure coil probes line up in boots when reinstalling coil packs
They are attached to the end of the HT leads.