Just got back after the holidays. Can't provide a link to the website yet as the shopping cart is published on my computer and not online. I was still testing it on my computer.

I will let you know what happens once it goes online.

It does seem strange that it works on 9 out of 10 computers. Hope someone has the answer to this mistery.

This is a long shot, but is it possible your monitor resolution has been set higher than it can actually handle?

I have done this on few computers and, even though the settings are accepted, the extra screen real estate due to the higher resolution is reserved offscreen. I believe the display of the desktop starts at the top of the monitor, so that might explain why your viewing of the product shot is lower on the screen.

Try setting your screen resolution lower and see if it effects anything.

9 out of 10 computers can't be wrong...

EDIT: Sorry just noticed at the beginning of the post that you mention you tried other resolutions - I would still try lower resolutions than you normally use - but only if you haven't tried that already.