According to spec,

http://java.sun.com/javase/6/docs/api/javax/swing/JTable.html#getShowHorizontalLines()

getShowHorizontalLines

public boolean getShowHorizontalLines()

    Returns true if the table draws horizontal lines between cells, false if it doesn't. The default is true. 


But code:
import javax.swing.*;
import javax.swing.table.*;


public class Test2{


public static void main(String[] args){


        JTable c = new JTable();
        if (!c.getShowHorizontalLines()) {
            System.out.println("FAILED");
        }else
        System.out.println("OKAY");
                

}
}


prints false if Nimbus LaF specified

C:\tests\JTable>C:\JDK\jdk1.6.0_10\bin\java.exe  Test2
OKAY

C:\tests\JTable>C:\JDK\jdk1.6.0_10\bin\java.exe -Dswing.defaultlaf=com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel Test2
FAILED

the same problem is with getShowVerticalLines()