You may have noticed Wikipedia has a new interface these days. If you run your own MediaWiki website, the obvious question in your mind is, how can I get these improvements on my site too?
This information is surprisingly hard to find, but the short answer is: you can’t yet.
How can I use Wikipedia’s new skin (Vector) on my wiki?
Vector is not available in MediaWiki versions prior to 1.16, and will be made default skin in 1.17.
—buried in the MediaWiki FAQ
As of the time of this writing (June 2010), 1.16 is still in beta, and 1.17 has no planned release date. Check the MediaWiki version lifecycle for current information.