Can't help you out completely, however
<a href="http://www.isc.org" target="_blank">www.isc.org</a> should have a version of DHCPD that you can use. I use it to serve my small little network. You can get the addresses to be static, by setting certain MAC addresses to certain IPs. That will get your static IP effect that you want.
In order to do IP Masquerading, also known as NAT (Network Address Translation) you can either make scripts and put them in the Library/StartupItems folder, or head over to <a href="http://www.versiontracker.com" target="_blank">www.versiontracker.com</a> and look up a utility called Brickhouse. It's a GUI that can let you set your firewalls and also enable the Routing features in OS X. I'm not sure if Brickhouse can help you out with Dial On Demand, However Internet COnnect may have an option to automatically connect to the internet when a request is made.
FileServing...
Go over to your Server Manager Application.. I think that's what it is, and you'll see options for which points to use as sharepoints as well as working with Users and Groups and things of that sort. You will also be able to enable FTP and DNS, and a webserver via that applications, but teh filesharing stuff will be there.
As for users and groups on the client machines.. Hope someone else can hel you out. Once you make a user on the Mac OS X Server, they can log in from their computer to access those files. I'm not quite sure about how Mac Networks are run or what the ideal situation would be... hehe.. sorry I learned Novell. =)
Hope I've helped out.. with a general view. If you really need specifics and exact steps.. kndonlee@mac.com