not that sure, but think mac not like odd number in ram if have one stick 1gb other should be 1gb too so if add a 2gb other should match. best check what max ram comp takes.
Your mac ether takes a total of 4 or 6GB, I can't remember.
It shouldn't matter that the memory sticks are mismatched. One may be dirty, so try cleaning out the slot with some compressed air.
Early 2008 takes up to 8gb. Id get a 4gb set (2x 2gb) and try a matching set of ram. If one of your slots is indeed faulty, look for a 4gb 667mhz stick to use in the working one.
By entering your serial number here to find specs for your model. (Be aware that some models can use more RAM than Apple shows. Check EveryMac or MacTracker to verify.)
not that sure, but think mac not like odd number in ram if have one stick 1gb other should be 1gb too so if add a 2gb other should match. best check what max ram comp takes.