ok here you go
"One reason is that Dell's $70 Nvidia GeForce4 MX 420 adapter -- the only alternative on the company's Web site; the full-size AGP cards available for the regular Dimension 4600 won't fit -- is stuck at the same DirectX 7 level as the built-in 865G graphics"
basically, due to the width of the case, if you want a graphics card then a half size card is needed, and according to the site in my second link, the only one dell provide is the GF4 MX420 which is OLD