I'm super-computer deficient but yesterday I added two products to the D20 Reviews product page. However, I don't know how to add the images for those products.
Assuming the image is posted somewhere online, and you're using a PC:
1. Go there, right click on the image, and choose Properties
2. Copy the URL that comes up (as Location: someplace)
3. Paste it into the spot on the product page that asks for image info
If it still gives you trouble, let me know what the products are and I'll take a stab at it.