Subdomain creation using .htaccess & mod_rewrite

This is a very simple project for someone who knows .htaccess, mod_rewrite, and apache extensively.

I have a PHP file when queried is of the sort:

http://www.usawebonline.com/search.php?site=cnn.com

I need it re-written to be

http://cnn.com/usawebonline.com

IF NOT possible to use their domain as the subdomain, acceptable alternatives are:

http://cnn-com/usawebonline.com (subbing "." for "-")
http://cnncom/usawebonline.com (removing ".")


I've tried many possibilities to achieve this but these is a detail wrong in every attempt, otherwise I would post what I have tried.

Please help!