Your best option is to add a conditional css reference which kicks in if the IE browser version is less than a given amount. For example if you add a new css file which contains styles specific to IE7. These commented out sections are IE hacks. This sytle sheet will not take effect unless the browser is IE7.
<!--[if IE 7]>
<link rel="stylesheet" type="text/css" href="/styles/main.IE7.css"" />
<![endif]-->
Then you need to adjust your styles in this style sheet to suit IE7.
Also sometimes IE is set to display intranet sites in compatibility mode. See this for adding a setting in the web.config which will prevent this X-UA-Compatible is set to IE=edge, but it still doesn't stop Compatibility Mode