Twilight Theme Different Behavior between FF and IE8

[pinoy_steal]

I use twilight theme on zimbra 6.0.6. My question are in firefox 3.5.9 the edge of the themes are curve but when I open it on Internet Explorer 8 the edge of the theme are straight. How I can modify this so that both firefox and internet explorer are the same looks and behavior. Please see this link to view firefox and internet explorer behavior on zimbra twilight theme

firefox:
http://img193.imageshack.us/img193/6...ightthemes.png

Internet Explorer:
http://img156.imageshack.us/img156/8...rertwiligh.png

Thanks