Customization sure, but it's a piece of cake. I have flash product images for thumbs, detailed images, you name it.
My current creation is simply just to use Deonya's detailed image mod (in the forum) and replace the last "if" statement to include the swf if there is no detailed image (it would generally include a thumbnail at that point) and then name all the product swf files using the product code and calling the swf by that.
If you want to put swf's in the detailed ... you might just consider adding a new template in the product.tpl and including it with a product code or id reference. The only reason to put it in the detailed images area would be if some products had a static image. I have modded a LiteCommerce site to either add swf or static images in the product image admin ... and X-Cart would be similar.
Just a little php and tpl modifications. Boomer (Cart-Lab) has an swf mod for X-Cart and detailed images, but he requires that you have him install it. I'd have bought it had he just given me the template and php code. So either think of a workaround, buy his mod or just use static images.
If that doesn't make sense, then try
http://www.cart-lab.com/lab/customer/product.php?productid=46
Boomer- if you read this, can't you sell the mod without the install charge?
- mike