You need to configure Apache to allow browsing user home directories.
The httpd.conf setting is "UserDir":
http://httpd.apache.org/docs/2.0/howto/public_html.html
Verify your configuration settings (httpd.conf, etc) are OK, verify that at least one user has a web directory (e.g. "~someuser/public_html/"), put a sample "index.html" in the directory, restart Apache ... and see what happens!
'Hope that helps .. PSM