Taking full control of another computer without an internet connection?

[Jag]

Really simple.
I'll presume you have Windows XP or newer on both systems.

Make sure both computers have NICs in them.

Connect an Ethernet crossover cable from one to the other NIC. Or you can connect Ethernet patch cables from each to a router, switch or hub.

Make sure the machine you want to control remotely has remote desktop enabled. Right click on my computer and check the tabs.

Open the remote desktop connection program of the system you want to control from and type in the IP address or machine name of the machine you want to control. Log into the remote system as if you are at it's keyboard.
Now you have full remote control of the other system.