redirect 301 from some URL parameter to other URL parameter?

Hello all,
I know this is not a WA related problem, but I'm breaking my head on the wall for this.

Basically I would like to redirect (redirect 301) 100+ URLs like:

http://www.mysite1.com/products.php?brand_id=2&line_id=3&fam_id=9&prod_id=71
to
http://www.mysite2.com/products_page.php?product=curasept-whitening-gel-dentifricio-sbiancante

I already tried to use redirect 301 in .htaccess but it doesn't work with URL parameters. It works only on simple pages like:

http://www.mysite1.com/page1.php
to
http://www.mysite2.com/page2.php

Is there a way to solve this?
Perhaps creating the redirect conditions in php on the old pages?

TIA for your help.
Tony

You could use php and do the redirect on the products.php page directly. It seems like .htaccess would work as well. You would have to use the RewriteCond line to matcht the url parameter portion. See:

http://statichtml.com/2010/mod-rewrite-baseon-on-query-string.html

Thanks Ray,
that's' exactly what I have done: I've set specific redirects in the product page.
Thanks for your help.
Tony