You, my friend are definitely a candidate for Linux. It was made for people like you. In a few cases, you'll need some extra hardware (example: Linux can't use those cheap Winmodems). But you'll find there's a ton of free software out there that is useful. The GIMP (GNU Image Manipulation Program), a Photoshop replacement, comes to mind. Star Office will be able to read your Microsoft Office Documents, and Star Office is totally free.

If Linux will require a learning curve for you, then I'd suggest initially installing a minimal Microsoft network to get started, and slowly bring Linux workstations on line one at a time OR you can install Linux as a standalone until you get the details of Linux networking down. It actually is not hard to network machines and ping and telnet them, but file-sharing will require either the installation of Samba or some other package like NIS. OR you can just put the shared files into the Apache server default web space for access through a web browser.