MEMO PARK. CALIFORNIA-If youwere born without a sense of direction, there’s a new device on the market ready to tell you exactly where to go. The ETAK Navigator is a com puterized system that may make the rumpled Rand McNally road map ob-solete. A driver inserts a cassette tape for the metropolitan area in question into the navigator, which then displays a map and the car’s location on a small television screen. After choosing a destination, the navigator plots the car’s progress on the screen. General Motors has acquired the rights for the system, but the original ETAK Navigator is now being sold by ETAK for $995.