Online help in IDL 7.0 may not work properly without taking special steps.

IDL's release notes have this to say about the fix to their help system:

  If you use the IDL Workbench, simply starting the Workbench
  with the

    idlde

  command causes IDL to use the newly-installed version of
  XULRunner. If you use IDL in command-line mode (without starting
  the IDL Workbench), you must start the IDL help server before
  starting IDL in order for the ? command to work properly.
  To do this, enter the following commands at the shell prompt:

    idlhelp
    idl

  Note that the IDL help server continues to run after you have
  ended your IDL session. If you prefer to shut down the IDL help
  server, enter the following command at the shell prompt:

    idlhelp -command shutdown

  Depending on your system, it may take several moments for the
  help server to start. Leaving the help server running speeds up
  the response time of the ? command significantly.