Installing drupal 6 with subdomains

Hi I have been using Drupal for a while now and i love it but I have a new website to build with subdomains which I have never used before.

My problem:

I need to install Drupal as normal; the site will have a LOT of content based on different departments within the main site. I also want to separate the departments into their own subdomains so they feel like they have their own websites and it will be easier for the users to find the relevant content faster, but all of their content will also be in the main site.

I have never set up Drupal will multiple sites before I have read the installation on how to but I was wondering is it possible to share the data from the main site and associate it with in a subdomain as well
Here is an example of what I want to do

www.domain-name.com/bat will be in the main site

And I want to be able to offer the department bat with a subdomain so they look like they are still part of the company but with their own site

www.bat.domain-name.com

I hope this makes sense and I appreciate any help on this.
Thanks in advance
dew