I tried following the very good instructions for multisite with subdomain provided by Kent Stanley here: http://drupal.org/node/107347
Here's my aim: I have domain.net. I want subdomain art.domain.net.
I created a second database and uploaded the drupal tables.
I created the folder "art.domain.net" in "sites" and placed the settings.php file in it with the appropriate modifications.
I created the directory "art" in public_html, put a fresh install of drupal 4.7 in there, then changed the file name to "old-art" before I ran symlinks.
I created a symlinks file which seemed to work as I got a blank page after calling it in browser.
<?php
symlink ('/home/user/public_html',
'/home/user/public_html/art');
?>
I couldn't find an explanation for what value "home" should be replaced with so I left it as "home" (like when I first installed drupal and was trying to figure out the value for "localhost" :) )
I couldn't rename "old-art" back to "art" because there was a new "art" in public html that seemed to mirror the whole site. However, I did successfully create the symlink, just not the one I needed. art.domain.net didn't resolve but domain.net/art now resolved to domain.net.