Well, a How-to...
Servers basically only differ from PCs in having other tasks. I've seen servers that to me were plain desktops, but I've also seen servers that were equipped with redundant power supplies, expensive RAID-arrays,
horridly expensive ECC Registered RAM and exotic OS-es. And I stand corrected: You can run a 16- or 32-core server on out-of-the box Win7 (and I read Win8 will support up to 64 cores), as long as the actual number of CPUs is not greater than two. Most Linux distros can help you here though, with a cheap and adequate solution. Windows 200x server is a bit harder to obtain for a nice price.
Basics:
* You need a network hub, but preferable a network switch to connect all PCs to your access point. A gigabit hub or switch is inexpensive nowadays, even when new.
* CAT-5 cables to connect your PCs to the hub or switch.
* Make all your PCs part of the same Workgroup. MicroSoft has the standard name 'Workgroup' for PCs in a workgroup.
Nice -to-haves:
Search for a 2nd hand 2, 4 or 8-port KVM switch (Keyboard-Video-Mouse), so you need but one monitor, mouse and keyboard. For two PCs a 2 port is enough.
Does not need to cost much via ebay or marktplaats (looks like mine). Make sure they sell it with cables, they are very expensive new.
Problem: new rigs come with USB - DVI connections, while the KVM switches in the 2nd hand department are mainly PS/2 - d-Sub (VGA).