using System;
using System.Drawing;
using System.Windows.Forms;

public class Form1 : Form
{
    ToolTip toolTip1 = new ToolTip();
    int lastHit = -1;

    Rectangle[] cars = new Rectangle[]{
        new Rectangle(100,50, 32,32),
        new Rectangle(200,50, 32,32),
        new Rectangle(200,100,32,32),
        new Rectangle(100,180,32,32),
        new Rectangle(10,50,32,32),
    };

    protected override void OnMouseMove(MouseEventArgs e)
    {
        int hit = -1;
        for(int i=0; i<cars.Length; i++)
        {
            if (cars[i].Contains(e.Location))
            {
                hit = i;
                break;
            }
        }

        this.Cursor = (hit >= 0) ? Cursors.Help : Cursors.Default;
        if (hit>=0 && hit != lastHit)
        {
            toolTip1.Show( "car " + hit, this, e.Location, 2000);
        }
        lastHit = hit;
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        using (Graphics g = e.Graphics)
        {
            foreach (Rectangle rect in cars)
            {
                g.FillRectangle(Brushes.LightCoral, rect);
            }
        }
    }

    [STAThread]
    static void Main()
    {
        Application.Run(new Form1());
    }
}

------解决方案--------------------

1、你可以用Cursor的静态属性Cursor.Position来得到当前鼠标的屏幕位置，不过你得把它转化
  成picturebox1中的坐标才好比较：
  Point p = picturebox1.PointToClient( Cursor.Position );

2、你也可以处理MouseMove事件，而不用MouseHover事件。在MouseMove事件中，就有鼠标的location了。