well for dvd's i think you have to do that under setup on your printers lcd screen, or i think it might also ask you right before you print onto the disk, i usually print from my memory card, so if your doing it a different way im not sure then.
as for photo's, again it kind of depends on how your using your printer, if your printing from a memory card then you'll have to change the settings under setup.
the printer also has a very nice troubleshooting page so check that out. also keep an eye out for the little lights around your color screen, there are buttons that only light up when you can use them
oh and if your printing from your computer, you really need to use the epson software, which can be downloaded from the epson website or from the cd that came with the printer.
for settings, when i hit print on the "main" page there are 5 different profiles
draft, text, text &image, photo, best photo
do not use best photo, make sure you select the right paper, higher quality paper may use more or less ink.
then for the advanced page make sure you have normal or below selected.
be aware that changing these settings could change the quality of your photo's quickly so some testing should be done to find the level suitable to you.
lastly, make sure you don't use any of the maintence tools unless you really have to, because that will use alot of ink as well.
im not sure why you would want to remove a partially used ink cartridge, but my guess is if you take it out ink will get everywhere.
and i know for sure that if you do remove it that you will not be able to put it back in at a later date as the ink will dry and you do not want ink clotting your lines.
i should also point out that you want ink carts in your printer at all times, never leave it empty and the ink will dry, this is also why if you run out of ink for one color that you are forced to replace it before continuing to print anything.
oh and one last thing, there is a chance your cartriges weren't actually empty, i guess epson put chips on the cartriges and i guess sometimes they go off when they shouldn't. but im not sure if thats true or not