Over LAN, Warcraft II only supports IPX/SPX. If you have XP x86 this is fine (Hell, even Vista x86 can be coersed in to using IPX if you give it XP's IPX drivers).
The only way I could find to make Warcraft II to use TCP/IP (which is a requirement if you use Vista x64) is to set up a psuedo battle.net server.
And diablo II does do TCP over LAN, so it will just work. But you can run a ladder or what not with Diablo II if you use a Battle.Net server (seemed quite popular at the last LAN I ran).
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