This is not a rollover but it is simple. Duplicate the first page with a larger image and link to that page from the smaller image on the original page. It should execute in an eyeblink since the background image is already loaded. You can allow your visitor to reverse the process by making another link from the larger image to the page with the smaller image. It's simple and intuitive for the user. Here’s an example that we built for a temporary website: Just click on one of the four sample textures, then click on the larger image that appears. http://www.tessfinishes.com/finishes.htm
There is a slightly more sophisticated version of the same technique on this page: http://www.tessfinishes.com/gallery.htm
If you really want a rollover, just make the picture box the same size as your large image and import the small image using the larger image as the rollover. I'm not sure how this would work for you because I am not aware of your specific context. Another thought would be to use a two-position rollover if you want the larger image to appear in a different part of the page.