I've had to say this too many times:
Computer 1 (server): Start up the dedicated server.
Computer 1 (server): Connect to 'localhost' (no quotes), using MTA:VC client.
Computer 2 (other player): Connect to the IP of the server with MTA:VC client.
To find the IP of the server:
Computer 1 (server): Go start -> run... -> type 'cmd', hit enter.
Type ipconfig in the window that appears.
One of those numbers is the IP of the server.