Shoutbox

You can make the window stay on top of other windows by specifying the TopMost attribute in the window's XML.
Example:

code:

---

<Window Id="...">
  <Attributes>
    <TopMost>true</TopMost>
  </Attributes>
  ...
</Window>

---

And by default it should appear in the center of the screen but to make it not movable you can disable the LockOnClick attribute.

code:

---

<Window Id="...">
  <Attributes>
    <TopMost>true</TopMost>
    <LockOnClick>false</LockOnClick>
  </Attributes>
</Window>

---

Can't test this at the moment but it should work...