I was getting “Microsoft Bus Driver should be loaded in your system before installing Realtek HD Audio Driver !” error message while installing my Acer Aspire 5051 laptop audio driver on Windows XP SP3.

Related information regarding this issue on Microsoft support site: http://support.microsoft.com/default.aspx?scid=kb;en-us;835221

Fix:
[*] Download the hotfix at Microsoft here.

The hotfix download link will be sent to your email address. Be sure to add email address hotfix-at-microsoft.com (replace -at- with @) or the domain microsoft.com to your safe sender list (whitelist). This will prevent the email from going to your junk folder. The email message also contains password to extract the hotfix file.

[*] Run the hotfix after downloaded.

[*] Download the newest driver here.

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Nov 17, 2008:
It seems Realtek has moved the content of the page, see this url for the newer version, its version R2.08 at the moment.

[*] Run the downloaded driver.

That should fix your audio driver installation.

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Nov 17, 2008:
One of my friend also having this issue when installing Windows XP SP2 with Realtek HD Audio on his PC. He confirmed that this hotfix fixed the issue.

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May 17, 2011:
For those who having problem with the Microsoft hotfix password, try mine. My download only for us-en only, if your installation differ, please download from Microsoft site.
Download: http://crushedge.com/files/hotfix.zip (2,943,124 bytes / 2,81 MB)