I copied a file that was a jpeg on there and it still wouldn't display in the camera >:
Maybe the folder you're putting it in is specifically for photos taken by camera. I'm not sure if it makes any difference, but I remember my brother's camera has two folders originally: one where the taken pictures go, the other was named misc if I remember well. So I guess check to see if you have any other folders.
And did you try putting videos to see if they show up?
I don't think is possible to transfer pictures from the computer to the camera. I know I never saw a camera doing that - the camera doesn't recognize the pictures. Cameras are very limited, they don't work in the same way as a computer.
After reading this, then only I realized you asked for computer pics to camera, instead I went to say camera to computer... so sorry about that ~_~;;;;
Umm, I look up a bit and here are some links that can help:
1) From Computer to Camera? [Archive] - Canon Digital Photography Forums
2) Answers.com - Is it possible to transfer pictures from a computer back to your digital camera