Ok, first of all thanks for the info. I got the trunk/boot/bonnet open, I opted to use the 'thin screwdriver in the lever area', i.e. sliding the solenoid across manually. Only thing I would mention to UK owners is that you're sliding it away from the middle of the car, not towards, but that's quickly worked out!
So anyway, I've opened it all up and am mildly happy...or kind of, I think maybe just relieved I can get to all areas of my broken car now
BUT.......and I do wonder if this is why my car died in the first place - to the right of the battery, there is a 'void' area with some elctrical items (I don't know what they are yet)....but anyhow.........that entire void was full of water. Right up to the bottom of the battery. I'm beginning to think the previous owner parked this car in the sea. I've drained it (more or less), but now need to find out what's housed in there....and then whether they will dry out in time (not counting on that as it's a typical British winter), or whether they will need replacing.
If anyone has any ideas what they are, that would be appreciated. In the meantime I've drawn a diagram of how to open the trunks, to suplement the guides below. It's crude but.....I tried. Also, photos of my water tank....argh, I mean, my car.
http://www.4vve.com/boxster/bootopening.htm