I am hoping for some insite on memory and whether or not what this can even be done.  I have some Optiplex GX620's that I am going to upgrade to 2GB of memory.  They have 4 slots and only 3 slots are being used right now.  I have 2x256 533 MHzDDR2  and 512 module.  I would like to take this memory and put it into an OptiPlex GX280 that has currently 512 of memory 2x256 DDR2 400MHz.

 

I am also wondering the currently memory in the GX280 can placed inside a GX270S that has 2x256 DDR 333MHz.  I am trying to save some $ here if I can reuse some this memory in between these machines.  We are hoping to only purchase a few memory cards rather than a whole batch. Advise is greatly appreciated.