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1. When I move a material node on the Material room, it just moves so slow. WHY??

From what I've read, they're working on that. Sounds to me like OpenGL hardware acceleration was left out of the material room.

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2) I play World of Warcraft on this PC and I get 60 FPS everywhere, and I find it amazing that my preview window on Poser 8 gets 0.5 FPS, even if I set it to display only the wireframe.

Becasue Poser's OpenGL calls barely use your video card for moving it all around - cameras, people, whatever. Poser uses your CPU almost entirely for that, and your GPU for VRAM and light, texture, and shader display. Not only that, but Poser uses only one core for display - it is not multi-threaded.
That's not unusual - that's the rule for most 3D apps, and will be until CUDA is more prevalent.
Games, on the other hand, make FAR more use of your GPU and use it in conjunction with your CPU.

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3) I have a Nvidia GeForce 9800GX2, 1GB of VRAM, 4GB of system RAM, and a Q6600 CPU (quad core). I've updated my video drivers to the latest, and still if I turn on OpenGL preview rendering on my Poser it will crash after a couple minutes of use.

That second GPU doesn't make a world of difference in any windowed app. It's like SLI in one card, and has to be specifically written for. Most modern games are specifically written for SLI and dual GPU video cards, but I can't think of a single 3D program that is.

Having said all that, you should be getting better performance, considering your CPU is a very good one. Why you're not, and why you're crashing is anyone's guess, and you should submit all that information, along with all your system specs, to SM so they can look into it.