alt not meta

i have

    (setq ns-command-modifier `meta)

to map the macintosh's command key to meta.

but the alt key seems to still also map to meta in some cases, e.g.
ALT-u, which used to set up umlaut, now does upcase word.  any ideas
on how to tell emacs to not grab that sequence (and all the other alt
sequences, such as for the euro currency symbol?

randy