“These are computer parts that look like they slot into the interior of a machine. The fact that they say "Poseidon Oil" and "Navigational Computer" on them lead you to believe they fit into a Poseidon Oil Navigational Computer.”
The NavCom parts are chips used for a specific type of computer. They activate some of the parts of the tanker, PMV Valdez.
The NavCom parts can be found in a locker on the third level of Vault 13 in Fallout 2.