While there are a lot of forum posts around this topic, I found the below extremely helpful since they give clear concise instructions on integrating StyleCop.
StyleCop in Visual Studio Express - http://refactoredmusings.blogspot.in/2013/01/using-stylecop-with-visual-studio.html
StyleCop integration in MSBuild - http://geekswithblogs.net/mapfel/archive/2011/11/07/147606.aspx