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It depends on how it's set up. Right now you have it redirecting to a directory on your server, instead of a true subdomain with it's own document root. Do you have CPanel on your server? If so, go to your Subdomain administration, click on Manage Redirection for the subdomain you set up, and click Disable Redirection. I've got several sites that do exactly what you're saying, and they're all set up the same way.

jW
 
No. AFAIK you can't get the result you want from Mod_Rewrite/htaccess alone. You need a new virtual host in the Apache config. If you're host is running any modern control panel and allows add-on domains it should be easy to setup. Just navigate the section called Add-on Domains (or its equivalent in the software you're using) and add whatever.yourdomain.com. It should create a new folder above public_html (depending on software again) so that your new subdomaiin will exist separately from your top-level domain.
 
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