Problem enabling .htaccess - apache

Question

I'm trying to enable .htaccess files on a Ubuntu server I set up. I changed the sites file from:
<VirtualHost *:80>
ServerAdmin webmaster#localhost
DocumentRoot /var/www
<Directory />
Options FollowSymLinks
AllowOverride None
</Directory>
<Directory /var/www>
Options Indexes FollowSymLinks MultiViews
AllowOverride None
Order allow,deny
allow from all
</Directory>
[unnecessary config code omitted]
</VirtualHost>
to
<VirtualHost *:80>
ServerAdmin webmaster#localhost
DocumentRoot /var/www/document_root
<Directory />
Options FollowSymLinks
AllowOverride None
</Directory>
<Directory /var/www/document_root>
Options Indexes FollowSymLinks MultiViews
AllowOverride All
Order allow,deny
allow from all
</Directory>
[unnecessary config code omitted]
</VirtualHost>
Now when I try to view a page in my browser I get a 500 Internal Server Error. Any ideas as to what my problem may be? Thanks for the help.
EDIT
Here is my .htaccess file:
RewriteEngine on
RewriteCond $1 !^(index\.php|images|css|js|robots\.txt|favicon\.ico)
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /index.php/$1 [L]
I checked the apache error logs as requested and it appears that the error being logged is:
[Fri Jul 10 19:39:12 2009] [alert]
[client 192.168.1.1]
/var/www/document_root/.htaccess:
Invalid command 'RewriteEngine',
perhaps misspelled or defined by a
module not included in the server
configuration

Answer 1

Bah... I didn't have mod_rewrite enabled. I feel stupid.