OK
Wasted another hour or two, uninstalling my GTX275 driver, running a driver cleaner and reinstalling 270.51 again, again it made zero difference.
After further experimenting I have discovered I can fix the green square texture problem by turning off the forest render completely. (I had it set to very low previously).
Having said that the game is still completely unplayable on a 2Gig WinXP system. In the hour or so I have been messing with this, I have got
1) Loading the london quick mission with 1 plane, still locks up on load screen
2) I had 1 instance of a crash that rebooted PC
3) 2 instances where I seemed to be flying OK at the start, but screen froze and locked permanently after 1 minute or less
4) shell casings from guns were rendering with huge black square around them (this one fixed itself after a reboot)
5) Changing some graphics settings says it needs to restart game. This then proceeds to crash, and you have to restart manually
those were just the ones I can remember, sighhhhhh
I need to take a break from this game its not good for my blood pressure
If you have a WinXP 2Gig machine, do yourself a favour and do not buy this game, you will regret it.
Regards Geoff