The very last version supported under Windows XP is Windows Live Messenger 2009 (Wave 3) Build 14.0.8117.416 as you pointed out. There have been no further build updates for Windows XP.
Besides I wouldn't want Windows Live Messenger 2011 (Wave 4):
"It brings features like a revamped interface which brings the "What's new" section of Windows Live to the new "social pane", similar to the way a social networking site presents updates. Among the new features are tabbed conversations, a redesign of the old emoticons, integration of Bing results, built-in video message support, HD video chat, in-line commenting of social updates, a new social photo viewer that supports commenting (for Facebook and SkyDrive photos), badges support, synchronised status updates, availability by categories, as well as integration with Facebook chat. However, several features had also been removed from the previous version, such as the removal of display names, handwriting tool, one-way webcam requests and import/export of instant messaging contacts feature."
They got rid of alot more than the crap they implemented. Look up Windows Live Messenger 2011 screenshots to see what I mean.