Well, your question isn't totally clear, but I think I understand what you're trying to do. Basically, you want your subdomain to point to a different directory, i.e. have a different documentroot, right?
If so, then you should use vhosts. It's very easy to setup. Here is the config I use for a subdomain on one of my sites:
<VirtualHost *>
ServerName brad.gagon.net
DocumentRoot c:/apache/htdocs/brad
</VirtualHost>
You will also need "NameVirtualHost *" (without the quotes) somewhere in there... I have it just above the vhost directives.