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The reason why the installers don't show VS 2012 as an available option is that currently VS Extensions don't support Visual Studio Express editions. This means that the UI Controls will be installed and you will be able to use them, but the Telerik VSExtensions for ASP.NET
will not be integrated with the Express editions of Visual Studio.
What you can do is to manually add the RadControls to the Toolbox using the 'Choose items...' dialog in Visual Studio.
I hope this helps.
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