Change in .htaccess file

I want to rewrite this url
http://mydomain.com/client.php?user=om&post=1

to subdomain

http://om.mydomain.com/client.php?post=1

The subdomain is already created and i want to show the post of related user through his subdomain url.

Please tell me the code for htaccess file.

 

ugly hack

RewriteEngine On
RewriteCond %{QUERY_STRING} user=([a-zA-Z0-9_-]+)&post=([0-9]+)
RewriteRule ^client.php.* http://%1.mydomain.com/client.php?post=%2 [R=301,L]

my personal preference is to route everything to my script and then do with query strings whatever you want