If you have had a “Microsoft Bus Driver should be loaded to your system before installing Realtek HD Audio Driver failure” error message when installing the driver for a Realtek HD sound card, then this solution is for you. Some of Realtek’s newer sound cards using the RealTek High Definition audio chipset have had the problem.
There are a couple of solutions to fix this Microsoft UAA Bus Driver for high defention audio error – both of which requires you to install Microsoft patches.
How to fix Microsoft Bus Driver error

Get the Microsoft bus driver free download KB835221.exe fix from Microsoft.
This fix is likely to solve the error for most sound cards, but you may not have it working yet. If so, follow the next method.
ADVERTISEMENTAlternate fix for Bus Driver error for Realtek HD cards

Download and install the Q888111 patch. This has two separate versions – download the appropriate fix from the links below.
For Windows XP SP2
For Windows XP SP1
Fix Bus Driver error on Windows XP 64-bit
Users of Windows XP 64 bit require another fix – Q901105. Download and install the patch to fix the error.
I also have the same problem and after following
microsoft cryptic instructions it didn’t solve
my problem. I found your explanation on the web and downloaded Q88111 for Xpsp2 extracted it found the famous missing file hdaudbus.sys installed it now I dont get that stupid message anymore. THANKS a million.