Apache VS IIS Securiyt model question

["mthompson" <mthompson () brinkster com>]

Hello,

I am doing research and I am stuck. 

Pitch: In IIS there is the ability to set permissions on a per website
basis. In other words the ability to limit access to files and
directories based on the users credentials that the website is running
under. Additionally, you would in turn add this user to a group and
apply group permissions to an object that needed to be accessed by more
than one site.

Question: Is there a similar security model for apache that would allow
credentials from a user to run a virtual website and access files only
for a specific virtual site.

Also, does any one have a diagram of the apache process?

Thanks,

Mike