RewriteRule for Domains and Subdomains

I'm working on some rewrite procedures for my websites.
Here's what I'm trying to get the htaccess file to do:

www.domain1.com/* -> /domain1.com/www/*
sub.domain1.com/* -> /domain1.com/sub/*
www.domain2.com/* -> /domain2.com/www/*
sub.domain2.com/* -> /domain2.com/sub/*

Code (markup):

etc...

and also:

www.domain1.com/shared/* -> /_shared/*
www.domain2.com/shared/* -> /_shared/*

Code (markup):

etc...

so here's what I have in my htaccess file so far:

RewriteEngine	on

# Shared Folder Rename
RewriteCond %{REQUEST_URI} ^/shared/([^.]*)
RewriteRule ^/shared/(.*)$ /_shared/$1

# Global Domain Rename
RewriteCond %{REQUEST_URI} !^/shared/([^.]*)
RewriteCond %{HTTP_HOST} ^([^.]+)\.([^.]+)\.([^.]+)
RewriteRule ^(.*)$ /%2.%3/%1/$1

Code (markup):

if I keep this in my httpd.conf file, everything works well
if I move it to the htaccess file in the root directory, i get loop errors:

[I]Request exceeded the limit of 10 internal 
redirects due to probable configuration error.[/I]

Code (markup):

Does anyone have any ideas what is going wrong?