If we talk about the help solution you can get as a result of finished compilation in DocMounter, it is an HxS help file in the MSHelp2 format used by Microsoft for MSDN in VS 2003/2005/2008. However, Microsoft introduced a new help format with the release of Visual Studio 2010. The final official name of this technology is "MS Help Viewer 1.0". You could also hear such names as "MSHelp3" and "MSHC". These things mean the same new format. "MSHelp3" was being used as a work name for the new format and now it is abandoned; "MSHC" stands for "MS Help Container" and it is the extension of the help package used in the new VS 2010 help system (which is in fact a zip archive with another extension).
The current version of DocMounter does not produce MSHC files directly as a result of one-command compilation, but you can get the required MS Help Viewer 1.0 package from the DocMounter output easily.
The first way - is to use an automated conversion utility such as MSHC Migrate Utility developed by MS Help MVP Rob Chandler. You just specify the input HxS and some output parameters as file names and titles, and it does the rest automatically.
Another way could be the following. DocMounter has an option which allows you not to delete the temporary files used to create the result HxS files. You can find the html sources for the future MSHC package in the subfolder that stores these source files used to create your HxS. These files need some corrections before they can be packed into an .mshc archive, and if you wish to do that by yourself manually - get them and process as you need.
You can find a more detailed description of the MSHelp Viewer 1.0 format and thus what you need to do with the html's in many places in the Internet. We recommend The Helpware Group web site being run by the same Rob Chandler - see, for instance, the following section totally dedicated to MS Help 3: http://helpware.net/mshelp3/