Hi Jamie,
This definitely works, and you should NOT leave out the .htm extension. That would be an error and should not work at all. My guess is that the output file name is not what you are expecting, probably because of the hyphens. There may be different characters instead of the hyphens in your output files, depending on your Help & Manual settings. Have a look in your WebHelp output folder after publishing and check the actual name of the corresponding topic file created there.
If you are using the current version of Help & Manual 7 (7.0.6 Build 3732) you can select the character to be used to replace spaces and other non-HTML characters in topic IDs. The setting is in View > Program Options > Editor, it is called "Auto-replace blanks in topic IDs with character: ". You can choose any character but it's best to use only a hyphen (-) or underscore (_).
If you continue to have problems mail a demo project and a copy of the skin you are using to
support AT ec-software.com (replace the AT with @) and we'll check it for you. Before doing anything else, however, please make sure that you are using the current version of Help & Manual 7. Since this is a new release, updates are going to be released quite frequently in the first period. You can check your installed version with Help > About. The current version is 7.0.6 Build 3732. If you need to update you can download the latest installer from
http://www.helpandmanual.com/downloads.html?upd
Just install on top of your current version to update.