If you're looking for an update to this addon, I've posted my current version here:
[link='http://www.wowinterface.com/downloads/info12361-SimpleMouseoverTarget.html']http://www.wowinterface.com/downloads/info12361-SimpleMouseoverTarget.html[/link]

I have no plans to update this addon on this site.

When you mouse over a character or creature in the game that is currently targeting something, it shows a second, small tooltip attached to the main tooltip with their target's name, level, and other info.

/simplemousetarget
toggle - toggle show / hide
on - show
off - hide
red - toggle turning the background of the second tooltip red if the target is the player
green - toggle making the second tooltip green if you are targeting the same the target
pos # (1-12) - relocate the second tooltip around the gametooltip.

Patch notes for Simple Mouseover's Target
Version 1.5
· Updated to 2.0 patch

Version 1.3
· Added option to change the second tooltip's background to green if the your target is the displayed target.

Version 1.2
· Players no longer show as 'boss' if they're to high level.
· Added option to change the second tooltip's background to red if the player is the displayed target. (on by default)
· Updated to 1.9 patch.

Version 1.1
· Added console commands to move it around the GameTooltip.
· Fixed minor text issue with the second tooltip showing dead boss mobs or mobs with no creature type.