Dynamic Virtual Hosts In Apache
Solution 1:
I suggest you have a look at the Apache website for dynamic virtual hosts. The other methods require a restart of the Apache server.
http://httpd.apache.org/docs/2.0/vhosts/mass.html
Solution 2:
I figured out how to do it after reading Dark Ninja's answer. Here's what my httpd-vhosts.conf file looks like now.
# Dynamic virtual hosts.
# See http://httpd.apache.org/docs/2.0/mod/mod_vhost_alias.html
UseCanonicalName Off
VirtualDocumentRoot /www/%0/htdocs/
I also had to enable mod_vhost_alias by uncommenting this line in httpd.conf
LoadModule vhost_alias_module modules/mod_vhost_alias.so