Full Collada 1.4.1 Support
The files downloaded from Mixamo in Collada format are compliant with the Collada 1.4.1 specifications and have been tested with the official Collada viewers. In order to open a Collada 1.4.1 file in Blender 2.49 (the last official release) you will need to install a plugin that Mixamo owns and maintains for the Blender community. Download the Mixamo Collada 1.4.1 Importer for Windows and MacOSX here:
Please report any bugs or other issues to firstname.lastname@example.org regarding this importer.
The importer scripts that are included in the zip files above need to be copied to your Blender user scripts directory. If you have not created a blender user scripts directory, create a directory somewhere (for example, 'blender_scripts' in your home directory) and set it to be your Python scripts directory in User Preferences > File Paths. Save your new default settings with File > Save Default.
For more information on setting your blender user preferences, see this overview wiki and this link for more in-depth information.