Redirecting non www URL to www URL

If you type yahoo.com in browser it will be redirected to www.yahoo.com.
If you want to do same with your website then put the following code to .htaccess file.

CODE:
RewriteEngine On
RewriteCond %{HTTP_HOST} ^optimaxwebsolutions\.com$
RewriteRule (.*) http://www.optimaxwebsolutions.com/$1 [R=301,L]

Where $1 is the first argument kind of thing like for example if you want to redirect

http://drupal.com/user => http://www.drupal.com/user .

Rewriting URL's with .htaccess

Rewriting product.php?id=12 to product-12.html

It is a simple redirection in which .php extension is hidden from the browser’s address bar and dynamic url (containing “?” character) is converted into a static URL.

RewriteEngine on
RewriteRule ^product-([0-9]+)\.html$ product.php?id=$1

For more reference on this refer:
http://roshanbh.com.np/2008/03/url-rewriting-examples-htaccess.html