Newbie need help to setup Clean URL

I just installed Drupal 6.20 on Ubuntu 10.04. Everything seems working fine except the clean URL. Please bear with me I'm new to Linux and Drupal. This is my environment:
- Drupal 6.20 on Ubuntu 10.04
- Apache 2 and MySQL, phpmyadmin installed and working fine

Steps taken to make clean URL working:
- sudo a2enmod rewrite
- confirmed with apache2ctl -M command and it's showing rewrite_module is loaded
- added

<Directory /var/www/>
AllowOverride All
</Directory>

to /etc/apache2/apache2.conf file (the original file does not have this entry)
- un-commented the following entries in .htaccess file

RewriteCond %{HTTP_HOST} ^www\.example\.com$ [NC]
  RewriteRule ^(.*)$ http://example.com/$1 [L,R=301]
RewriteBase /

What else do I need to do to make clean URL to work? I thought I did everything, but it seems something is still missing!!! When I tried to enter a clean URL as suggested by others (http://localhost/admin/settings/clean-urls/), I got page not found error. Right now I have clean URL page grayed out.