3000x3000 pixels doesn't change, no matter what your ppi/dpi settings are - it'll always be 3000x3000.

ppi is a file in the computer - the actual pixels - 3000 pixels by 3000 pixels.
dpi is a printing term - it's how many dots per inch are actually PRINTED by a machine.

We use them loosely - interchanging in day to day conversation - and in speaking in terms about the size of an image, they mean the same thing. I think Rendo was just being technically correct in what they asked that you send - it's a digitial image file so hence the ppi terminology.

And Incarnadine is right - look at your pixel sizes - 800x600 is TEENY - 2400x3000 is nice and big. The ppi/dpi doesn't mean squat until you actually go to print. Just make sure your pixels are enough to cover the sizes they want to print.

Hope this helps-
-Lew ;-)