Has anyone have any idea how could this be accomplished?

I have this mod installed and working great on my site, i have a few pages that i want to permanently redirect.

Note: I am moving the products i have in another site (not Zen Cart) to a Zen Cart, i want to keep the urls that was indexed from the old site by doing a redirect 301. the domain name will be the same.

This is my code in the .htaccess

Code:
Redirect 301 /Old-Product-Name_p948.htm http://www.mydomain.com/New-Product-Name-p-621.html
I am getting Page not found and the url in the browser look like this after i try to access the old redirected page.

http://www.mydomain.com/New-Product-Name-p-621.html?seo_url=Old-Product-Name_p948.htm

If i changed the code in the .htaccess to
Code:
Redirect 301 /Old-Product-Name_p948.htm http://www.mydomain.com/index.php?main_page=product_info&cPath=35&products_id=621
it works fine, but since this mod is doing a redirect on
http://www.mydomain.com/index.php?ma...roducts_id=621
to
http://www.mydomain.com/New-Product-Name-p-621.html

then i would like to get my redirection to the end result and stay away from the link or double redirection.

Any idea?