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.