Microsoft has releases a Windows Vista Service Pack 1 release candidate to the public. It is not the final version of the update to their latest operating system, but it reportedly does improve network performance.
Quotes
"Service Pack 1 is a very important milestone because it addresses many of the key issues that our customers have identified with Windows Vista over the last year both, directly and through programs like the Customer Experience Improvement Program. With Service Pack 1, we have made great progress in performance, reliability and compatibility."Windows Vista Team Blog: Announcing the RTM of Windows Vista SP1 (February 4, 2008)