SharePoint 2007 Site Permissions

Hey,

I was wondering if anyone knows how to put different permissions on different sub sites…

So i Have my main Site Called “COMPANY”

With 4 subsite (tabs) IT, Marketing, HR , Sales

Everytime i go into the IT site for example and add a group to the permissions it seems to add that group to the entire “company” site.

What i’m wanting to accomplish is giving each site (tab) particalur groups, Like only hr accessing hr site, i.t accessing i.t..

Hope i made sense , let me know if this is possible.