A: Network, using crossover cable.
B: Network, using patch cable if both machines have auto-configure NICs.
C: Network, using hub or switch, use patch cables.
D: Ad-Hoc wireless Network
However you do it, if both computers are XP machines, install protocol "NWLink IPX/SPX/NetBIOS Compatable Transport Protocol" in both computers. Found in network card properties, "Install" , "Protocol" and choose the above to install.
No re-boot needed.