Easy(?) way: SP3 includes the drivers you need for the actual sound drivers to work. ;>
Don't want to go SP3 yet?
Go here:
http://support.microsoft.com/kb/888111/
There's a link at the top to 'request hotfix'.
I find it quicker to grab it from cnet:
http://download.cnet.com/kb888111-exe/3000-2110_4-104699.html
Quote:
Microsoft UAA Bus Driver for High Definition Audio
Microsoft UAA Function Driver for High Definition Audio - Realtek 880/860
Microsoft UAA Function Driver for High Definition Audio - CMedia 9880
Microsoft UAA Function Driver for High Definition Audio - Realtek 280
Microsoft UAA Function Driver for High Definition Audio - Realtek 260
Microsoft UAA Function Driver for High Definition Audio - Realtek 261
Microsoft UAA Function Driver for High Definition Audio - Sigmatel 9772
Microsoft UAA Function Driver for High Definition Audio - Sigmatel 9770
Microsoft UAA Function Driver for High Definition Audio - Conexant Waikiki
Microsoft UAA Function Driver for High Definition Audio - Adi 1986
Microsoft UAA Function Driver for High Definition Audio - Adi 1983
Microsoft UAA Function Driver for High Definition Audio - DDKCodec
End Quote