OK, here goes... I had a lot of to'ing and fro'ing so this is a summarised version of the instructions I eventually used and found actually worked (notwithstanding some comments included below too).
need:
The following links etc basically describe the following process:
Hacking the XBOX - A Pre-Cursor to being able to install XBMC
Essentially this installs a new interface on your XBOX and allows you to open it up to FTP files from your PC via your network (or by simply plugging it in to your PC's ethernet port using a crossover network cable).
1. Make an Action Replay device.
2. Download and install Action Replay software.
3. Get your home-made Action Replay working with the correct driver.
4. Getting hold of the hack files.
5. Hacking the XBOX.
6. Opening up the network on the XBOX.
Installing XBMC
1. Sourcing the XBMC program files.
2. Connecting via FTP on your PC to your XBOX.
3. Moving the XBMC files on to the XBOX.
4. Job done!
A memory device to get the Hack Files on to the XBOX
First I followed
these instructions to make a an Action Replay device. I bought
this card for £3.41 (I specifically sourced an original MS card because I suspected it may be the only type where the back was screwed on (and therefore removable) but I may be wrong).
Now I download and installed the latest version of the Action Replay software from
here.
I then plugged the memory device in to my PC and Windows 7 took over and (unhelpfully) installed a default driver. I spent a while sussing this one out... Windows recognised the device as a disk drive but would not let me update the driver (Windows kept telling me that it had already installed the best driver). However... I then spotted that it also recognised the device under USB devices too. I updated this driver, browsing manually to "C:\Program Files\Datel\Action Replay XBOX\Drivers".
Launch the Action Replay software and the big "AR" logo in the middle of the screen should turn green if you have successfully set up your memory card. If not it will remain grey. I noticed it sometimes took a few seconds to change colour (but no more than 15 seconds tops).
Getting the Hack Files on to your XBOX
These are the best instructions I found covering the whole process through to installing XBMC. However, I referred to
these instructions for specifics about mIRC and FTP software, albeit the mIRC software interface and therefore instructions are old so require a little intepretation... Also, the instruction to type “/msg xbins !list” is no longer valid. You simply type "!list" (without the quotes). Final comment on this area... The aforementioned (linked) Lifehacker instructions tell you to get XMBC from the second XBINs FTP server (and the message back from XBINs that you get when you type "!list" suggests the same. However... I could not get the second server to connect so tried the first server for XBMC and found it under XBOX Applications.
Specific comments aside, this is more or less what I did to hack the XBOX and install XBMC.