IP address with username

Hi Guys,

I am able to access all the sites in the server but I am unable to access the site with http://IP/~username. I can't even access a single site in the server with the ~username. I tried it with the / and without / as well at the end, but no luck. I have the entry in the httpd.conf file

#
# 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>


what am I doing wrong? any help would be appricated.