Set up Ubuntu Server 12.04 for my office

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http://askubuntu.com – As i have great interest in Linux, I suggested my GM to update my office server to Ubuntu. He agreed to buy a new server(Hardware) after explaining him the good things about Linux & bad things about windows. The scenario is: The main server will be Ubuntu 12.04 LTS (where I should create a domain & users on domain) The old server (which is win 2003) is going to be an application server. Around 30+ windows (Both win 7 & vista, 32 & 64 bit) machines should connect to the domain & be able to access the shared folders on Ubuntu server. I really appreciate some help as i d (HowTos)