mod_rewrite - is it possible?

From: Piotr (piou_at_gaztea.pl)
Date: 11/15/04 

Date: Mon, 15 Nov 2004 13:08:26 +0100

I have domain:
www.main_domain.com/index.php?userid=23&parametr1=2&parametr2=3
Under this address tere is an template site for many users. Personal site
is identified by userid.

I want to do short subdomain for all users like this:
www.hisowndomain.com?parametr1=2&parametr2=3
but this short address should be call main domain (with masking long
address):
www.main_domain.com/index.php?userid=23&parametr1=2&parametr2=3

www.main_domain.com/index.php?userid=23 --> www.hisowndomain.com

I have access only for .htaccess file (no httpd.conf) - is it possible to
do it by mod_rewrite? What can it be done?