[VM] How to view HTML mail?

[Skip Montanaro]

How do I set up VM to properly display HTML mail messages (or hand them off
to something which can)?  I'm running VM 8.1.93a with GNU Emacs 23.1.1 on
Mac OS X.  I see a variable, Vm Mime Text/Html Handler, which is set to 
auto-select, but when I attempt to view an HTML mail it says something like
"inline display by nil failed".  (Sorry, the message doesn't stick around long
in the minibuffer and view-lossage doesn't display it.)  I see w3m and w3 as
choices but don't know what either one is or how to install them (does GNU
Emacs have a package installer like XEmacs?  If so, I couldn't find it.)  I
don't have lynx.

Thanks,

Skip Montanaro