I again tried to install the Komputerbay ram in my D600 but it won't work...however did manage to install another 1Gb stick that was in the HP.
So now I have 1.5 Gb ram in my D600.
I'll probably decide which one I'm going to keep as my main and as a backup from the 3 running laptops I now own in the week to come,the least powerful one (still decent enough though) will go to a mate who only needs it for browsing the net and is currently using a borrowed laptop.