Domain Mapping .htaccess redirect 301

Hi,

I have a multi-site with domain mapping plug in. We uses sub-domain network set up for mini-sites. We just mapped site1.domain.com to http://www.anotherdomain.com.

I'm wondering how do we set up redirect 301 in htaccess for old URLs from http://www.anotherdomain.com?

For example i want to redirect http://www.anotherdomain.com/?id=160&sid=55 to http://www.anotherdomain.com/first_page/

How do i do that in my htaccess file ?

Thanks