I didnt look at what anyone else has said except your first post.
This is not a RAM issue.
Try to increase your Virtual Memory, if that doesnt work, let me know and we'll see what else there is.
It sounds like your virtual memory is getting pushed to its limits by Spores virtual graphic needs.
I've had a smiliar problem with older PC's on much lower specs than my current one, This is just one of a few things to try.