I have an online store called www.frattoys.com.
The problem is when your customer tries to check out they cannot access the drop down box that has the credit card selections. Everything is greyed out. The issue is with IE9 not being compatible with Magento. The solution is to trick IE9 into thinking it is IE8.
This is a two step process:
First, add the below line to your head.phtml file right below your title tag - (app/design/frontend/Your Template(usually default)/Your Template/template/page/html/head.phtml).
<meta http-equiv=\"X-UA-Compatible\" content=\"IE=8\" />
Second, find your .htaccess file and add the below two lines of code -
BrowserMatch MSIE best-standards-support
Header set X-UA-Compatible IE=8 env=best-standards-support
This should work. It did for me.
If you need any help with this you can call Johnny from www.tranquilblue.com