I want to do load testing inside Visual Studio Professional 2012. According to the tutorial here http://msdn.microsoft.com/en-us/library/vstudio/ms182551.aspx, under F
I believe you cannot do that. Web performance and load tests are only available within Visual Studio Ultimate edition. See http://www.microsoft.com/visualstudio/eng/products/compare
In summary, there are five version of Visual Studio
Ultimate, adds web performance and load testing.
Test professional, has some test tools but no development tools.
In addition to @AdrianHHH answer: Running Visual Studio 2015 you will find it in the renamed Enterprise Edition.
VS2015 reduces to three versions:
Basic info at Visual Studio 2015 pricing
In detail at Visual Studio 2015 Licensing White Paper