As an update... here's the status of the 64 bit Vista install.
I was able to get Vista 64 installed. I re-rendered one of the previous scenes where threads kept dying in 32 bit Vista. In 64 bit Vista, the render succeeded without any issues using all 4 threads. Note that I installed not only Vista 64, but an additional 4GB of RAM for a total of 8GB of memory in the system. So, apparently, with the scenes I was creating, somewhere along the way during the render, Terragen 2 is running up against a 32 bit memory limitation. I'd like to see a fully native 64 bit compiled Terragen 2 to take full advantage of the 64 bit system.
However, there is an OpenGL issue under 64 bit Vista that isn't present, to this degree, in 32 bit Vista. The OpenGL library of the 8400GS Nvidia card drivers (in my system) is VERY buggy in 64 bit Vista. Some OpenGL bugs also existed in 32 bit Vista, but did not affect Terragen 2. However, in 64 bit Vista, simply moving around in the node network (dragging the screen around) is enough to crash the Nvidia OpenGL library and, by association, Terragen 2. This crash also leaves the entire video driver in an unstable state which requires a reboot. This OpenGL crashing issue is a known issue that Nvidia has been working on for several months now (and has been unable to resolve). I ran into this issue with Poser originally. Poser, however, thankfully supports SreeD (a software based OpenGL-type engine). So, I can use Poser without crashing.
Note that I have the most recent Nvidia drivers installed from 9/25/2008 and these bugs are still present.
Apparently, this OpenGL driver crashing issue may affect many cards in the 8XXX series of Nvidia GPUs. It may also affect other Nvidia card models outside of the 8XXX series. The extent of this OpenGL bug in the Nvidia drivers is presently unknown. According to SmithMicro (Poser), Nvidia is aware of the problem and they are working to resolve it.
At this point, I'm considering the purchase of another GPU for my system... most probably an ATI card where this OpenGL issue is likely not present. I'll just need to find one that has HDMI and supports 64 bit Vista.
Thanks.
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Brian