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#11
Setting up a domain will require a Server OS and a decent machine. On the domain, from what you are saying you want, will also need to be your file server. Another thing that I'm not sure if you understand or not is that you will only be able to use your credentials if the machine is added to the domain. So you will have to set up your domain. Create the user accounts. Then add every machine that you use to the domain. (A domain is not the easiest thing in the world to set up and configure. It requires its share of maintenance as well.)
If the domain is down, you can still log in using your credentials, but your data will not be available.
What JDobbsy is suggesting is a much better solution. To lock down your folders you just need to make sure that only your account has access to it. Simple as that. But this will mean that you must login to each computer with that account every time, but it sounds like you want that anyway.