Is your base Poser install 4.03? There was an update apart from the update for large memory systems. Have you tried running Poser before installing the memory update? Other than that I don't know. 750GB is way beyond the environment Poser 4 was designed for but I don't know if that would cause the problems described. You might try creating a small partition of 50GB or so and try Poser there. Does sound more like a memory/graphics drivers/etc. issue though.

PS prepare to be chided by some for using Poser 4 - apparently it's akin to a moral defect :-)

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken