Alt vs Meta key in Emacs

[Joe Riel <joe.riel@incep.com>]

I use a pc104 keyboard, the bottom row looks like the following:

<ctrl-L> <window-L> <alt-L> <space> <alt-R> <window-R> <menu-R> <ctrl-R>

Using xmodmap I swapped the <ctrl-L> key with the <caps lock>.
In emacs (under X), 
  <window-L> acts like a <meta> key, 
  <window-R> doesn't do anything (using xev it shows up as "multi-key")
  <alt-L> and <alt-R> do nothing (they act as <alt> modifier keys, but
that
  does nothing in emacs).
  <menu-R> behaves as <meta-X>.

How do I change these keys?  I tried using keysym in xmodmap,
but my first attempt did not work with emacs.  A search of the
emacs info pages, web, and Debian HOWTOs wasn't a lot of help.

I currently would like to have the <alt-L> and <alt-R> keys 
act as <meta> keys in emacs (in the long run it might be better
to have the window keys become <meta> keys and the <alt> keys
be a new modifier, however, I'm switching from NTEmacs where
<alt> is <meta> and that's what my fingers want to type.)

Thanks for any pointers,

Joe Riel