There are 2 main contributions that you will need to apply to a standard oscommerce install, the first one that i shall talk about today is called Ultimate SEO URLs.
What this osc contribution does is rewrites the standard dynamic URLs to more SE friendly and keyword rich URLs
in short it would turn a url from this:
www.domain.com/product_info.php?cPath=1&products_id=1
to something more descriptive like this:
www.domain.com/article-directory-turnkey-script-p-1.html
You can can clearly see how the second URL would be more descriptive and better picked up by search engines.
The installation is quite straight forward and well documented by Bobby AKA Chemo, but If you need help installing the contribution you can contact the store owner of this oscommerce hosting site. I highly recommend his work.