Refile to a different Org file?

["Raymond Zeitler" <r.zeitler@ieee.org>]

I'm trying to change the value of org-refile-targets to enable me to refile
to the other files that make up my agenda view.  Its value started out as
just nil, which worked exactly right for one file because I was able to
refile to all the *categories* in ~/todo.org, using tab completion, and it
didn't get confused by tags or heading names.

So far I've used customization to put this into the appropriate section of
my .emacs:

 '(org-refile-targets (quote ((org-agenda-files :maxlevel . 1) (nil
:maxlevel . 1))))

This doesn't work the way I expect.  I figured out that I can refile if I
specify the heading "Tasks" and the filename.  But I cannot refile to any
categories other than the ones in ~/todo.org.  And sometimes I get choices
that I don't want where the heading starts with the same text as the
category name.  BTW, I use unique category names across all files using this
structure:

* Tasks
#+CATEGORY: DM_Tasks

My setup files (.emacs and .orgmode) are a modified version of John
Wiegley's tutorial setup (sans the above customization) and can be found on
the Emacs wiki at this link:

http://www.emacswiki.org/emacs/RaymondZeitler

Is it possible to get the original "nil" behavior while searching through
all agenda files?  Or should I just use unique Level 1 headings in each
file?  How do other folks use Org-mode with multiple files?

Hope this makes sense.

Thanks

--
Raymond Zeitler <r.zeitler@ieee.org>