I have seen a plugin for Joomla, which works in the following way:

You define keywords, e.g. "car", "engine", "clutch", etc.
These words all have a specific product page.
You link the word to the matching page.

The plugin is then loaded on EVERY page across the site.
When it finds the word "car", it automatically creates a link.

So:
"This car is great"

becomes:
"This <a href="/page.php">car</a> is great"

So, you will get a tekst with plenty of links to other pages, which improves google rating.

Is there any script out there that can do this?