[annoyed]

There is actually more than just the inside corners missing.
IE shows several bits missing including the right hand side verticle border for the second and third product, whereas Firefox shows the box side correctly (still missing the inside corners as you said).
You need to keep looking at the code for the products because the rounded corner coding is working fine for all except these boxes which suggests it's one slight error in coding somewhere.
Without being able to test it right now I'd suggest firstly looking at the code
<h1 class="color_a"></h1> and maybe commenting it out to see if it changes anything because you aren't actually adding any h1 tag to the box in this instance.
Another possible change would be to add &nbsp: to the <h1> tag so that it atleast creates a space in there I have had success with both but I have always used edited versions of this code.
The right hand menu still goes off the screen in IE (but not in FF) maybe the two issues are connected (although possibly not) but it might be a good idea to work on one at a time and if the box error fixes the menu fine, if not attack that once the boxes are fixed.