Are you talking about the root of the site, e.g. http://yourIP/ results in a 403? If so, what does the DirectoryIndex directive look like for the corresponding <Directory> entry in Apache's .conf file (possibly httpd.conf, though there can be numerous .conf files dedicated for certain areas)? Are you perhaps missing an index file and have directory listings disabled?
EDIT: Also, check your Apache error logs - they will tell you exactly what the problem is, e.g.:
[Wed Oct 19 13:11:26 2011] [error] [client 127.0.0.1] client denied by server configuration: /path/to/htdocs/
or perhaps:
[Wed Oct 19 13:11:39 2011] [error] [client 127.0.0.1] Directory index forbidden by Options directive: /path/to/htdocs/