Im using onMouseOver on a image to make it go bigger when you rollover it, but then when you do it moves the entire page down. How do you get around this?

This is one of those times when position:absolute is needed.

You have to take the img element out of the document flow;

Without seeing your code (it does help us you know);

insert a placeholder element the same size as the image positioned relatively, then put the image inside it but positioned absolutely. It should locate itself at 0,0 of the parent container.
Then when it expands it will expand over the surrounding elements.
You may have to juggle with the margins and z-index a little.