As far as I know the keyboard characters for accented characters only really
work for the accented characters in the Western European languages.

If the character you want is a unicode character and exists in the font you
want to use, you should be able to assign a keystroke or button to it (not
sure about this on MacOSX, but do you actually mean Word 2004? Or are you
running Word 2000 in a windows virtual machine  under MacOSX?) If it's Mac
2004 you will probably get a good response to this question in the Mac
Office group.

If you want to invent a new character and re-use it, you can try
a. using an { EQ } field to superpose two characters. You can save the
field as an autotext if you want to re-use it, but generally speaking you
will need more than one version of the field if you need to use the
character in various different point sizes
b. creating the character you need and turning it into a picture (but I
don't know how to do that on Mac). You will lose quality and probably find
it harder to align the character
c. creating a new font with just the characters you need. (I don't know how
you might do that on Mac).

Peter Jamieson