Hello Christophe,
Running help in Infocenter-Mode basically means running your help as a
standalone rcp-application on a server. Your RCP clients can then merge
this remote help into their local help.
Info on how to run the helpsystem in Infocenter-Mode can be found under
the following links
http://www-128.ibm.com/developerworks/opensource/library/os-eclipsehelp/
http://help.eclipse.org/help33/index.jsp?topic=/org.eclipse.platform.doc.isv/guide/ua_help_setup_infocenter.htm
Once the Infocenter is running you can tell your application to use remote
help by adding those lines
org.eclipse.help.base/remoteHelpOn=true
org.eclipse.help.base/remoteHelpHost=<help-server>
org.eclipse.help.base/remoteHelpPath=/help
to your plugin_customization.ini file.
The problem with that is that it seems to be impossible to reference
remote help pages from the contexts.xml