After reading through the whole thread I'm not quite sure what the goal is at this point.. If you are planning to connect to the server box from 3 other computers and run things on the server, you won't even need gigabit networking. If you also plan to sometimes use the server to transfer lots of data to two or more of the 3 computers, RAID1 might be worth it. RAID0, 5, SSD's, and raptors wouldn't help, though.
If FreeBSD has too steep a learning curve, try OpenSolaris. The only install in the same category of ease is OpenBSD. There will be some commands you have to learn to set things up in Solaris, but a lot of them will be very easy (e.g. "share /rpool").
"So a quad core proccessor 4gb ram pc should do good for 3 sessions at once?"
You'll have to think about what you want to do with the sessions. A quad running 3 sessions could be massive, massive overkill (for web, email, etc.), or almost completely worthless.
Based on your posts, here are some thoughts:
Only get a quad if you find a good deal, otherwise a good dual core CPU will be plenty. 4GB of RAM will probably also be plenty.
There are OS's designed for exactly what you want to do. But none of them are made by Microsoft; some of their OS's will do what you want but since they aren't designed for it at all, they will suck (think pizza delivery on a train, it's powerful/reliable enough but just makes no sense).
Whichever OS and setup you choose, there will be a _steep_ learning curve for you.
Are you sure you need to have one server with 3 terminals running on it?
Also, what is this for?
If you narrow it down, serving files and/or remote desktops (and what they'll be used for), people will be able to give you valid advice.