How to generate an HTML report from PartCover results .xml
There is a tool you can use to generate a HTML report:
https://github.com/danielpalme/ReportGenerator
Here you can find an article how to integrate the tool into MSBuild:
http://www.palmmedia.de/Blog/2009/10/30/msbuild-code-coverage-analysis-with-partcover-and-reportgenerator