IE9 issue

Hi,

I’ve been building a site using this theme on my mac at work over the past few days. Today when I went to view it on another computer, this one being a pc running windows 7 with IE9 installed, the theme seems fine with the exception of the grey border and rounded corners that the main content appears in. On the PC the corners appear darker at the top, whilst the left hand side and top lines are light whilst the right hand side line is so feint it can hardly be seen. it looks fine on safari on my Mac.

any suggestions please?

thanks