First off, I totally agree with the previous poster. Do not use Fedora 9 for a server with what you are trying to do. Even beyond the fact that F9 has some issues, just in general Fedora changes too much to be used with a production server. You will find yourself in almost continuous "upgrade mode". As KKJensen suggested, try CentOS. It is basically the same as RedHat Enterprise Linux; it is rock solid for use with a server.
As far as what you are trying to accomplish you need to define it a little better. You mention printing. What you could do here is setup Samba and CUPS on the Linux server. There's tons of documentation out there on how to do this.
For Internet/Intranet activity, Squid is a proxy server and if you set it up properly it can log all activity. Keep in mind that you will have to find a way to make all the client PC's use the proxy server, so this will involve changes to your network. By default Squid will not require any authentication, but can be setup with Samba for AD integration. Here is a link
that I used to set this up on one of my servers. You also may want to look into software that can work in conjunction with Squid to restrict and limit Internet usage; Squidguard is one that comes to mind.
As for the specific Samba questions:
Security Model - depends on what you really want to do. ADS provides full AD integration, but can be a bit tricky to setup (at least it has been for me). DOMAIN security model is more of like a NT domain model, but it does work with AD and is much easier to setup.
ADS Realm - This is basically your fully qualified Active Directory Domain. So, YOURDOMAIN.COM, YOURDOMAIN.LOCAL, something like that. - You only need to set this up is you end up using ADS security
ADS Domain Controller - This is the IP address (you may also be able to use the FQDN) of your Active Directory Domain Controller.
Template Shell - I always just use /bin/bash. Honestly I'm not really even sure what this is used for.
The Samba documentation is excellent. I'd recommend going to the Samba web site and starting with the Official HOWTO.