Great job, pretty impressive! Got to try it out!! (:
But a tip for the social engineering part - I would recommend changing the text to something like:
Critical Vulnerability in Windows Vista, Windows Vista, Windows 2000 found 12/10-2008.
Prior to using our free services, please patch to avoid spreading malware into our network.
OS Universal patch available here: download or visit Microsoft's site regarding MS08-067
That would feel more real instead of faking a genuine Microsoft Update.