running files from subdomain but show main domain in browser

The VirtualHost directive allows you to set up the three different subdomains on a single machine (if that's what you're looking for).

The ServerAlias directive allows you to associate the same VirtualHost server with several different domain names.

Check the manual for more about those directives: http://httpd.apache.org/docs/2.2/

Is this what you're trying to do?

i have read the manual, but im not able to write the right config file. Its hard for me as i have no expirience in this area. Can you please write an example?
i have tried with the following(paths are ok)::
<VirtualHost>
ServerName www.d1.com
DocumentRoot /www/sub1
ScriptAlias /cgi-bin/ /www/sub1.com/cgi-bin
</VirtualHost>

Thanks

My mistake.  I missed the fact that you want to do this in an htaccess file.  The <VirtualHost> directive will not work in htaccess according to the manual (probably because htaccess works on a per-access basis and virtual hosts must be set up when the server starts).  You must put them in the main configuration.  Because you're asking this question I'm assuming you don't have access to the main configuration.

If you can alter the htaccess rules of the default domain then you can use rewrite rules, but I'm guessing that if you could do that you'd probably have access to the main configuration and be able to use VirtualHosts.

yes. i dont have access to main config files. Thats why i needed solution in .htaccess file (using rewriting rules) which can be placed in any folder.