Small Images & Huge images

I am doing a printed sign and banner site

I need the images on product details page for the banners to be much larger than the signs…say 500 wide x 150 deep.

I dont want the normal sizes on the other sections of the site to be affected. Can I do this by altering the template or creating a new one and assign the “banner” category to the newer template which may allow the larger sizes just for the banners?