OK guys 'n' gals, how to get yer door trims off.
The very FIRST thing you need to do is go to the Holden dealer and pick up as many of the little red lock knob clips as you're going to need. The only time I managed to remove this clip without destroying it, was when I actually damaged the lock knob itself.

They're only about 50c each anyway.
Now that you have your new clips, you can set to removing the lock knobs. My method is to just drill a 2.5mm hole in the middle of the red bit, and screw a short self-tapper in there - then pull on the screw to remove the clip. Once the lock knob is removed you can see a screw behind there - remove it.
Now you need to remove the interior door handle. Use a small flat-blade screwdriver to prise out the plug, and remove the screw holding it in. Give it a jiggle and the handle assemby should pop out. Have a look how this works - the "other" end of the handle bit just engages in a loop in the end of the pull-rod. While you're looking in there, you'll find ANOTHER hidden screw - remove this one as well.
OK - talking about the FRONT doors now, you also need to remove the triangular trim panel near where the mirror is. Just swing that out to unclip it.
Now, around the edge of the trim there are several more screws you'll need to remove, but at least they're not hidden away - although the ones along the bottom edge can be a little hard to spot. If you have all the screws out you should be able to unclip and swing the trim out from the bottom, then lift it upwards to disengage it from the top of the door bit, at the bottom of the window ledge. For the drivers side front door you'll need to disconnect the mirror switch, and for the back doors you'll need to do the same with the power window switches as well before you set the trim aside.
The factory speakers are attached to a moulded plastic plinth - the drivers attache to the plinth with 3 screws, and the plinth attaches to the door with 3 screws. All 6" speakers will drop straight into the cutout, but most 6.5" units will require a little work. They fit, but you need to remove about 4-5mm around the inside edge. I use a jigsaw for this, then clean it up with some coarse grit sandpaper.
Putting it all back together is basically just the reverse, but make sure when you're dropping the trim down onto the window ledge that the clips are engaged along here correctly, otherwise you won't be able to push the trim down far enough to lock it in right. Also don't forget to wire any electricals back up before you put all the screws back in!
As a side note, whenever I'm running amplified speakers in the doors, I run new wiring to them. I leave the factory wiring taped up inside the doors, but prefer to run higher quality cable to the new speakers. (leave the factory wiring there though, so it can be reconnected if/when required) Getting a piece of decent wire through that convoluted rubber thing (between the pillar and the door) can be a real pain-in-the-arse, but it's do-able. I use a piece of the thick whipper-snipper line about 30cm long with the wire securely taped to it - the nylon line finds its way through there relatively easily, and once it does you can then use it to pull the wire through. Gently!! Also, getting new wiring through to the back doors is even MORE painful, as the front seatbelt reel needs to be removed so you can get to the point where you'll pick up the wire in the pillar.
Anyhow, hope it helps.
Cheerz!