Picture to SD card to Camera?

I have a MacBook Pro, a SDHC card and a Nikon d5000
My old camera is the Kodak z915

Okay, so what I'd been doing is putting my pictures in iPhoto, editing them, then putting them back on the SD card.
Worked great!
But then I got my new camera and I tried to do the same thing, the camera won't show that their there in playback.
I put the SD card into my TV and it showed that they were there and worked fine, same thing with my computer and iPhoto.
Is it just the camera not reading them?

Different camera brands format memory cards in different ways. Your new camera can't understand the formatting that is used by your old camera. By the way, you really need to stop using your memory cards like that. They are NOT intended to be used as storage devices in that way. One of these days you will put a card with good photos in a device only to find out that said device formatted the card automatically and erased your photos in the process.