Zen will automatically pick up any file with a .css extension in the css folder of your template, regardless of the name. Renaming to styles_ajax_image_swapper.css.bak should do the trick.
yeap, any css file with styles_ as its prefix will be loaded on every page. Actually, if you're into site speed improvements, you can move everything inside syles_ajax_image_swappers.css into product_info.css so they will be loaded only on product info page.
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Check on www.WebExtremeCustomiser.com for my modules (free contribution):
AJAX Image Swapper
AJAX Banner Swapper
Fixed Navigation
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