For the AC move, all you need is a new bezel (Part No. 996.552.339.00 01C). This is only about £3 to buy. There are 2 screw holes already in this area that the AC Controls fit straight into. Here is a very quick howto.
First of all, remove the stereo. You will need the 2 stereo release keys to do this and once you put the keys in you will have to give it quite a tug. I used 2 screwdrivers in the eyes of the removal keys to lever it out. Once out, remove the wiring from the back of it. Now you need to remove the 2 switch panels. These are easily removed but be carefull not to damage the tabs on the back by pulling them out too roughly. Just use a flat blade screwdriver preferably with masking tape on the end to stop it damaging the surrounding dash trim and push it close to the bottom of the switch panels. With a light, gentle levering, it will pop out at the bottom. You will then be able to pop the top out with just finger pressure. You do exactly the same with the left hand switch panel but to completely remove the panel you will have to disconnect the 4 sets of wires from the back of it. These just pull off but they do require a little bit of pulling. It may be easier just to slide a flat blade scrwdriver under the wire connecter to lever them up a little bit. The one for the cig lighter pulls off fairly easily. You can move the AC Controls without removing these switch panels, I just found it a little bit easier with just that little bit more room as it can be quite a pain to get the AC Controls wiring down the back.
To release the AC Controls there are 4 x Philips head screws to undo. The top 2 screws actually hold the AC Panel in and the bottom 2 hold some detachable brackets in place. Undo the 4 screws (top 2 first) and you will then be able to slide the AC Conrols forward. Be ready to catch the brackets as they can fall. You can now pull the wiring connectors from the back. Again, these required quite a bit of pulling pressure to get them off. There are 4 connectors on the back but don't worry if you forget their positions as they will only fit in one place on the AC Controls.
Now you can remove the radio surround. This is held on by 4 torx20 screws. When you take this off, beware that there is a wire attached to the back of it on a spade connector. This is for the radio alarm. If you are fitting a non-Porsche unit then you will probably just want to tape this up so the alarm does not beep everytime you set it. This now leaves a nice big hole for you to get your hand into.
Now you need to remove the undertrays at the bottom and the 'batwing' which is just above the gearstick. The easiest way I found to remove the 'batwing' was to take the 2 side panels off that are to the left and right of the 'batwing'. These just pull off and are on some sort of pressure clip. Pull it from the back pulling towards you and it will slide off. You now have full access to the 'batwing' that you can pull fof with your fingers. Again, you don't need to remove these panels as you can get a screwdriver in and prise it off. It just makes it easier and less chance of scratching it.
You now need to take the 2 trays out. It took me a while to work this one out but basically, the top tray holds in the bottom tray so you must take the top tray out first (some people may have a CD holder here which I dont have, but I would imagine that removal is the same). The tray just pulls out. You may have to give it quite a tug. The lower tray will then also pull out but again needs quite a tug. Be carefull, I managed to take skin off a couple of my fingers when it eventually came out.
You will now be able to feed the AC Control wires down the back to the lower tray. Seperate the wire blocks to do this as it makes it much easier. It takes a bit of time to find the right route but its a simple enough job. Once the wires are down the bottom you can connect them back to the rear of the AC Controls. The connectors will only fit in one place so you cannot get it wrong. Once the wire is on, you can push the AC Controls into the hole and use 2 of the screws that were holding it in when it was in the top slot. It only requires 2 screws when it is in this slot and you will not require the brackets that were holding it in at the top slot. Once its in you can push your new facia over it and the move is done.
I am just about to install a Pioneer F900BT in this space and the best way I found of doing it was to buy a kit for it that contains everything required to do it and has a nicely finished bezel with the Porsche wording on it. I will not post a link to Ebay as these links disappear after a while. If you are looking for the kit, then just go to Ebay and type 'porsche double din'. There will be a few that come up with the Boxster being one of them. The kit has everything you need to fit a double DIN unit (well for Pioneer anyway, it may need to be adapted for a different make). If you are purchasing the kit, then there is no need to buy the new bezel for the AC Controls as you get one with it. The full kit is just over £100. This does involve cutting your current radio surriund though. If you ever wanted to put the original stereo back you would have to obtain a new surround.
The AC Controls can be moved to the next slot up but that involves extra work. I decided not to do that as I eventually want to put a CD holder there anyway. To do it, you can use the original bezel but you need to file or sand down the corners as the bottom corners of the hole are rounded.