Photo Resolution on ipad 2

If you have smaller, compressed images on your PC, they will actually take up more space on the iPad. iTunes creates a few versions on your pictures when it synchronises which is why on first sync with the new photos, you will see the message 'optimising pictures' for a while. I think it generates 3 images, one thumbnail, one full screen and another over sized image that has been optimised for zooming.
I'm not sure how large, full resolution images are handled i.e. if they are downsized and actually use up less space.

I don't think the answer is completely straightforward. When you import photos through iTunes it will reduce the resolution of them down to around 2000x1400 so that will reduce the file size. However at the same time iTunes decompresses them so the iPad has an easier time displaying them; which will increase the file size.

The best plan is probably just to stick the photos on and see. If you run out of space iTunes should just tell you it couldn't fit all the photos on.