Also 960mb of ram is not much at all I'm afarid.  You should considering upgrading if at all possible.

Until then - check out the textures you are using on your Daz characters.  A lot of them come in around 3000x3000 to 4000x4000.  This eats up memory very fast.  If you have a paint program you want to consider reducing the texture sizes :) Maybe around 1000x1000 or even smaller if they are not being used for close ups.