Rollover and Swaping images

i am a novice at web design, but i am trying to swap an image on a rollover and when clicked on, another image will change on the page. was able to get this to work but once i move to another image, the image that changed when clicked, goes back to the original. hope this makes sense. all in all i am trying to work on a portfolio that has smaller works by me and when clicked on they show in a "theater." if anyone can help, thanks.

Are you using javascript or CSS to control the rollovers?

Whatever the case, post your code here (in [code ] tags), or post a link so we can see what you have so far...