Connect Two computers with out any additional hardware(router,switch,.etc).It just needs a CAT5 Cross-Over cable.CAT5 Cross-over cable explained below.

TO make CAT5 cross over cable you need
1.CAT5 Cable of required cable,
2.RJ-45 Clips 2 nos,
3.Crimping tool(to crimp RJ-45 Clips on both ends of the CAT5 cable)
with this you can make your cross over cable at your place.

you can also purchase Cross-over cable at your nearest store .

More simplest way is purchase one RJ-45 Cross-over adopter(shown in the figure) and use this adopter at one end to your existing lan cable(CAT5 Stright cable) which makes Cross-over connection.

Connecting TWO PCs :

 If both the PCs have LAN Card / Eathernet Card then simply connect your Cross-over cable directly with both the ends.

If LAN Card / Eathernet Card not available use “USB to RJ-45 Convertors” to connect CAT5 Cross-over cable.

Before physically connecting two PCs ensure both the PCs are in the same Workgroup. To keep both PCs under same Workgroup, in

–WINDOWS XP : Right click on  “My computer” -> click on “properties” ->click on ” computer name” tab ->click “change” button ->type unique name in “workgroup” box.

–WINDOWS Vista : Open “Control panel” -> type “workgroup” in search box(right top) -> select “change workgroup name” ->click “change” button ->type unique name in “workgroup” box

–>WINDOWS 7 : type “workgroup” in search box at start menu -> select “change workgroup name” ->click “change” button ->type unique name in “workgroup” box

WINDOWS automatically finds new network (or new PC) and now you can view each other computer at Controlpanel -> Networks by computer name and also can access all the shared stuff including shared files,shared folders,shared printers,shared scanners,..etc.