I posted before that Beta 6 doesn't like me when using a terrain with the European tile set; lots of artifacts like grey rectangles in the sky or my CBM plane icon turning into a cloud. I thought maybe my download was corrupted so I did a separate clean install, but it had all the same issues. I tried out the Karelia terrain and noticed another symptom: when flying above the dense forests only rectangular blocks of trees render and if I quickly look elsewhere then look back, a different rectangular block of trees render. This is nothing but a wild guess, but it appears to me that my 32 bit Windows XP install cannot handle that many trees. It's like it runs out of memory or texture count and just doesn't render large blocks of objects, perhaps even the majority of them. It also appears to affect frame rate: even though I have a reasonable graphics card, a 2GB HD7870, and a fair CPU, a 3GHz E8400, my frame rate in a tank deep in the forests of Karelia can drop as low as 3.
I am beginning to think my 32 bit Windows XP OS isn't going to handle AH3. Looks like a triple boot (XP, Ubuntu, Windows 7) is in my future.