Well it has been around for a couple years as the G2 series started it and that is starting to get almost out of warranty for us so that is why I said years.

The Compaq SmartStart Scripting Toolkit can enable and disable this feature I believe.

Here is a link with some further information about it.

http://h18004.www1.hp.com/products/servers/technology/hyper-threading.html

http://h18004.www1.hp.com/products/servers/technology/hyperthreading-ossupport.html

An article here on the Windows .NET Magazine site says that it is not supported via WMI.
http://www.winnetmag.com/Article/ArticleID/40228/40228.html