How do I open an Internet browser window?

I want to open up a browser window for my users when they click on a link in my game. I am using this:
system_ "help.html"
This does not do anything in version 1.14. What's wrong?
Thanks

OpenURL "http://www.google.com"

Does this work (on all platforms) for local files (e.g. "help/index.html")? What about email ("mailto:aaa@...")?

Mailto: works for me.
I'd imagine local files will work as well.

They both work here, on Windows XP, but I'm wondering about Mac/Linux