Okay, here's how to do it:
First, make sure you have an image library that contains each of the category images, and create a lookup field in that library to the Category list's Title field. That way, you can associate each image with a category
Create a blank web part page. Open this page in SP Designer, and click in a zone, and add a data view web part. Pick your image library where the associated images are store.
In the data source library, click the drop-down on your image library, and choose "Show data". Select only the Name field, and choose to insert selected field as... Multiple item view.
Put your aspx page in split screen, so you can see the code. Select the first cell that contains the name of the first image in the library. In the code, within the <td> (that cell), paste this:
<img border="0" src="{@FileRef}" />
Then, this will display only the images in your table.
Save, and go open this web part page in your browser. Export the web part, and then go to the category.aspx page. Import the web part there.
Then, create a new web part connection from your Query String URL filter to this new image library web part. For the filter field, choose "Category".
VOILA!
FUN STUFF!
Laura Rogers
http://spinsiders.com/laurar