Before you install this Beta release, back up all MP3 files that might be accessed by the Windows 7 – The first hotfix for Windows 7

Here’s the warning by Microsoft for those who intends to download and install Windows 7 beta:

To protect your MP3 files:

1. Before you install this Beta release, back up all MP3 files that might be accessed by the computer, including those on removable media or network shares.
2. Install the Beta release of Windows 7; download and install the Update to Windows 7 Beta (KB961367) located on this page.

Microsoft releases Update for Windows 7 Beta (KB961367) in MSDN and TechNet Subscriber Downloads page to fix the bug and protect the MP3 files for users who use the Windows 7 beta build 7000. The KB961367 is not be published on Microsoft Download Center yet.