now everything is like am attempting to see the www.b.com

it will document cause of a.com

how do i change it out as both a and b should work.? can one use alias.?

like checking id there's bb in request visit document cause of bb otherwise visit document cause of aa.

So what can i actually do to do this?

You have to run Apache with 2 VirtualHost elements Body for any.org and something for b.com.

Each can indicate it's own DocumentRoot

The config is going to be something similar to

<VirtualHost 127.0.0.1>
   DocumentRoot "C:\My Sites\Site1"
   ServerName a.com
</VirtualHost>

<VirtualHost 127.0.0.1>
   DocumentRoot "C:\My Sites\Site2"
   ServerName b.com
</VirtualHost>

Find out more at http://apptools.com/phptools/virtualhost.php and http://httpd.apache.org/docs/2.0/mod/core.html#virtualhost