In your httpd.conf file you can setup aliasing which means:
As an alias causes your users to be directed to /var/stuff/coolstuff when they type:
SO, if you wanted to set it up that way I don't see what the problem would be. The other option that you mentioned would be to symlink which I do believe should work pretty much the same (make sure exec priviledges are there on the directory that you are symlinking to). To symlink:
ln -s /home/pictures/toms/cat /var/www/htdocs/postnuke/gallery
Should work (of course all the directories used in my examples should be changed to the actual directories).