During installation, entering the "Configure Printer" menu, I want to enter my printer, a HP DeskJet 600, explicitly listed under "HP DeskJet/DeskJet Plus", but only can choose resolution 300x300, although this printer is capable of 600x600.
yes, but the original deskjet/deskjet plus isn't, hence the limitation. Try using a different driver (which the description says, no less), or editing the config files manually.