Try something like this
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME}/index.html !-f
RewriteCond %{REQUEST_FILENAME}/index.php !-f
RewriteRule ^(.*)$ index.php/$1 [L]
</IfModule>
this code assumes the site is at the root of the domain