Example:

#
# UserDir: The name of the directory which is appended onto a user's home
# directory if a ~user request is received.
#
<IfModule mod_userdir.c>
UserDir public_html
</IfModule>

Or on a per virtual machine basis:

<VirtualHost *>
ServerAdmin root@somehost.com
DocumentRoot /usr/local/apache-ssl/htdocs
ServerName host.domain.org
UserDir users
ErrorLog /var/log/apache-error.log
CustomLog /var/log/apache-access.log combined
</VirtualHost>

If UserDir is not defined, ~ will not be translated to some directory name, but remain top-level.

Cheers,

Keith