First, make sure that you add a collider component to each part which you want to be an active rollover.

Next, add a GUI Texture GameObject to your scene (from the GameObject menu). Rename it to "Rollover Text Display" (exactly, case sensitive).

Now create a new Javascript script, name it "RolloverItem", and paste this in:

var rolloverText = "";
var rolloverColor = Color.red;
private var originalColor : Color;
private var textDisplay : GUIText;

function Start() {
    originalColor = renderer.material.color;
    if (rolloverText == "") { rolloverText = gameObject.name; }
    textDisplay = GameObject.Find("Rollover Text Display").guiText;
}

function OnMouseEnter() {
    Debug.Log(textDisplay.gameObject.name);
    textDisplay.text = rolloverText;
}

function OnMouseExit() {
    Debug.Log(textDisplay.gameObject.name);
    textDisplay.text = "";
}

Finally, add this script to each object that should have rollover text. If you don't specify some text in the "Rollover Text" field for each item, the object's name will be displayed. You can so adjust the rollover colour.