The answer to the question, why would you need more than 4GBs of memory is that I use Lightwave and the Adobe CS3 suite of tools and usually all at the same time. Oh and I do the normal admin stuff while the programs are busy doing their things. They seem to be able to use whatever memory I have available and my work is generally very large, high-resolution for print graphic files. In the past and I suspect it will be so in the future, more memory meant faster everything. So, even with two processors and 4GB of memmory there seems to be room for improvement. Hence my thoughts about getting 4GB sticks and replacing the 2GB ones already in there.
Thanks for all the thoughtfull replies and maybe I am just an old hardware nut that has loved to upgrade memory since my first TRS 80!
Dan