I'm remiss in not posting this earlier, my apologies. If you're running the Windows 7 Beta, you will want to immediately patch the system to fix a serious flaw that could cause the system to ruin your MP3 files. Here's some info from the KB article as well as download links for both 32-bit and 64-bit versions of Windows 7...
An update is available for Windows Media Center and Windows Media Player in Windows 7 Beta
An update is available for Windows Media Center and Windows Media Player in Windows 7 Beta. This update addresses some issues with Windows Media Center playback, recording, and MP3 file support in Windows.
Playback and recording issues that are fixed in this update
- Protected tuning sources, such as OCUR and ISDB, do not function correctly.
- MHEG (iTV) in Europe does not function correctly.
- Recording of a series may fail after some time if the system was upgraded from Windows Vista and the recording of that series was set up in Windows Vista.
- Windows Vista DVR-MS recordings do not play back in Windows Media Center or in Windows Media Player.
- Windows Media Center may become unstable when you perform recording operations.
An MP3 file support issue that is fixed in this update
Every time that metadata is edited in an MP3 file that already contains lots of metadata in the file header, some audio at the beginning of the track may be lost permanently. Up to several seconds of audio may be lost.