Photoshop 7.0 and Leopard

I recently installed Leopard to my imac. I have Adobe Photoshop 7.0. When I tried to open photoshop after installing Leopard, I get the following error message. "An unexpected and unrecoverable problem has occurred because of a program error. Photoshop will now exit." Now everything I created in photoshop gets the same message when I try to open it. I'm thinking I need to upgrade my photoshop program to Photoshop CS. When I look up the system requirements it says Mac os 10.4. Will this solve my problem or are my files lost forever?