Hiya.
I did another reinstall...now it's working MUCH better.
I'm using XP-64, and the only thing I've found is every now and then the program kinda 'hangs' for a second or two...usually when moving the camera around or moving an object. I've only checked to see if it works (maybe 3 minutes of playing), so when I get a chance in a few days I'll do a bit more wandering around in it.
Thanks for your help!