You will never get an IE7 or IE8 rendering engine to ensure full compatibility with HTML5, CSS3, and other modern technologies. They are simply not capable of it.
However, there are some hacks, tools, and plugins that can help you with this.
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IE7.js > Dean Edwards Selectivzr - Javascript, IE CSS, . , , IE. (IE7.js IE)
CSS3Pie - IE, CSS border-radius, box-shadow.
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