what memory do you already have ? and most of all what processor do you have in the machine, no point in having heaps of memory if you only have a small processor, look at the splash screens as the pc starts and you should see the processor speed or you could download a processor identifier program if you dont know what speed it is, to see how much ram you have right click my computer and click properties its shown in the bottom right of the box.if adding more memory you will also need to know the type of memory you already have ie sdram etc etc .