Xml image navigation

Hi

I have a image uploader using a xml file. which uploades catagory thumbs initially and once clicked on the catagory uploades the products and when clicked on a product thums uploads the main image.

i have do upto cat thumb uploading and cant figure out how to upload the prdct thumbs in a click event. can anyone help me i have all the files uploaded.

please gimmi an explaination cos i need to learn how it works

Thanks
Nameez