The Galaxy Tab is pretty much like any other android device. You can transfer images to it, but not directly from, say, your Camera.
It does not have USB ports on it for external devices, like thumb drives.
Connecting to a NAS, out of the box, also really isn't possible. The device does not support mounting NAS (NFS & CIFS) out of the box. You could use some file manager applications that do support SAMBA, like Astro File Manager. But you would have to copy the file to the Tab before you can watch a video or listen to the mp3 for example.
With that said, it would be possible, if rooted, to install the modules needed to mount NAS shares. I have done this with my Galaxy S device. The advantage of being able to mount the share on the system level, I no longer have to copy the files over to the device, since the shares are mounted on the device, it "thinks" they are actually on the device.