HHS files are used by MS' HTML Help Workshop (HHW) to compile samples into .chm files. At the time of writing there was a single titbit of info out there on the web.
Below is an example of a hhs file
[Example1] ID=Example1 DistributionMediaDestination=MyProject\Example1 DefaultClientCopyDestination=\MyProject\Example1 SourceLocation=Samples\Example1\