Rewrite username from site.com/user to subdomain user.site.com ???

[MechanisM]

Please!! Help me to rewrite username from: site.com/user to subdomain:
user.site.com !!

Now my .htaccess looks like this:

RewriteEngine On
Options +Followsymlinks
RewriteBase /
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^.* - [L,QSA]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^.*/images/(.*)$ /images/$1 [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^.*/uploads_user/(.*)$ /uploads_user/$1 [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^([^/]+)/?$ /profile.php?user=$1 [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^([^/]+)/([^/]+)?$ /profile.php?user=$1$2 [L]

.... etc.