Hi guys
I had to work this out and it took me a while and there's nothing in the forums to date. So here is the issue and solution.
Issue is that you want to redirect a URL like this:
"http://www.bluewolf.net.au/zencart/index.php?main_page=index&cPath=257" to one like this

A normal redirect will drop everything after the ? being the query string.

To achieve this edit your .htaccess and insert:
RewriteEngine on
RewriteCond %{query_string} ^main_page=index&cPath=257
RewriteRule ^zencart/index\.php$ http://bwcommercial.com.au/index.php?main_page=index&cPath=6 [R=301,L]