Thanks, stickyb.
I'm happy now that I have 3GB RAM working properly since it is adequate for my needs (my most extreme usage typically peaks at about 2.8GB) and I only upgraded from 2GB to 4GB since I wanted to install balanced pairs (4x1GB).
The linked article you kindly posted is however very interesting and in turn it links to an excellent series of Blogs on memory management.
Cheers,
XV105