Bzzzzt. There are already rootkits for Vista.
This was debunked just a couple weeks ago. There are no Vista rootkits if you leave UAC turned on.
http://www.securitywatch.co.uk/2008/05/29/vistas-uac-spots-rootkits/
http://www.pcworld.com/article/id,146387-c,vistalonghorn/article.html
http://www.hardocp.com/news.html?news=MzI2MTMsLCxoZW50aHVzaWFzdCwsLDE=
If you turn off UAC, Vista will be vulnerable to rootkits, but this is like turning off anti-virus software and then complaining that your system is vulnerable to viruses. A silly, stupid argument.