Well, it's working
It was pretty lucky I guess, because I borrowed a HDMI lead and a HDMI -> DVI adapter from a friend and plugged that from HDMI graphics card out to DVI monitor in, and then plugged graphics card DVI out to monitor VGA in with another adapter, and that didn't work - after modifying the kexts I booted and got a flicker and then a black screen - so I buttoned it off and decided to try putting the DVI to VGA adapter at the other end of the cable, but it was the wrong gender, so I just left it. Then I booted again, and this time it worked
So, my set up is: HDMI cable out from graphics card to DVI in on the monitor via an adapter, and the DVI cable out from graphics card to nowhere
But I'll leave it there just in case xD But it's great that I only have to use one monitor port, because I can still have my Xbox connected via VGA
I hadn't quite realised how much sexier the whole OSX interface is with a proper resolution and fell acceleration xD And I have managed to install the program that I needed to, so all is good.
The only problem I do have is that when the display goes to sleep automatically (I.e. Monitor standby) it doesn't wake up :? But I guess that's a DSDT/ACPI power state thing to be fixed?
Thanks again - I had nearly lost hope for getting this Hac working; I've been trying to enable graphics for three months - and now it works like a charm ^_^