I'm enable to install RedHat 6.1 from a hard drive. After searching the available packages but before presenting the list the installation program crashes with an "Unable to umount device resource busy" error. In the news site I read about someone that solved the problem by choosing one of the predefined configurations with automatic partioning. In my case I'm also getting a "Autopartitioning FAILURE" error (using custom installation method) which I think is the cause for the device busy error. The autopartitioning component fails and doesn't release the device.
I've just found out that I had a corrupted package in the RPMS directory. Download it again and the problem went away.