Create or copy a standard desktop shortcut for OFP. Then right-click on the shortcut and select PROPERTIES. The following example is based on Windows 98 shortcut properties. In the TARGET field, specify:
"C:\Program Files\OFP\OperationFlashpoint.exe" -connect=server.ip.address -port=port_number -nosplash
Replace "server.ip.address" with the IP address of the server you wish to directly connect to. The "port" setting is optional and defaults to 2234. Your file path to OFP's EXE file may be different than in the example above. For inform about -nosplash, look here.
If you've got OFP: Resistance, you can choose to specify on the above command line whether the server you wish to connect to is using OFP: Resistance's Windows sockets (default) or Microsoft's DirectPlay interface. You can indicate this by appending -sockets or -dplay respectively to the command line.