Realtek have released new drivers for the AC97 card.
Dated 24th January 2007, these drivers are not yet up on Windows Update.

[url]http://www.realtek.com.tw/downloads/downloadsView.aspx?Langid=1&PNid=23&PFid=23&Level=4&Conn=3&DownTypeID=3&GetDown=false#AC[/url]

These are proper drivers and I can confirm you will no longer get the error
message in control panel that the drivers are not designed for Vista.

During setup you will get a message to say the drivers are unsigned, but
accept and continue.

YAY no more annoying message about my sound.