I have no personal info on whether it will accept/use more than 4GB. Just reporting the Dell published specs, what I go by.
Dell, in many cases, uses a modified motherboard chipset and the AMD or Intel published specs do not always apply. For example, I had a Dimension E510 (5150 model is identical). It came with a D820 CPU and according to the Intel specs it was compatible with up to a D960 CPU. But, because of the Dell custom chipset implementation a D945 was the fastest Dxxx CPU that would work in it. We had reports, on the Dell forum, of users trying the D960 and it would not boot.