They're all here: http://www.dell.com/support/drivers/us/en/04/Product/optiplex-gx280
(I just restored a gx270). Nice computer....heavy, though.
Weird, when you type GX280 in the dell search box at the top on this page: http://www.dell.com/support/drivers/us/en/04/Product/optiplex-gx270
if you click the recommended drivers link, it takes you to the page for the gx270, not gx280.
So, after I clicked the "RECOMMENDED" (drivers) link, then, I just clicked up in my Internet Explorer address bar, and changed the last gx270, after I clicked on the recommended drivers link, to gx280, and hit enter.
I guess Dell had a bat link, there, where it said:
Click here to find the most up-to-date drivers for your product.
Please click above to find the latest drivers.