I have one stick of 1GB in the 1st of 4 slots. Can I add 2 more 1GB sticks by removing the one stick & putting it in the 3ed slot & adding 2 1GB sticks in the 1st & 2ed slots for a total of 3BGs? Or do I need to have ram in all in all 4 slots for the upgrade to work.?
Yes, theoretically you must be able to add two more 1GB modules with the existing without any issues. Perhaps, you may require a BIOS update but it should work regardless of that. IMO, going with 4GB of memory is better. If you can try matching the speeds of the existing memory.