When I upgraded my RH 6.0 machine with the (awesome) graphic installer, I had a Linux partition yet unformatted. When the installer searched for partitions with Red Hat installed, this partition caused a Python error (visible by switching the virtual console) and the installer hung. Formatting that partition with mke2fs solved the problem, and the upgrade completed smoothly.
I have had the same kind of problems with NTFS formated partitions : mount fails (in my case because there is no NTFS module in the kernel and in the previouly described case because the ext2 partition is unformated). The mount is tried during the initial localisation of a linux root filesystem. This bug is 100% reproductible using either graphic or text installer. A simple fix for me was to change the partition type from 7 (HPFS/NTFS) to 17 (Hidden HPFS/NTFS) using fdisk, running the installer/upgrader and changing back the partition
*** This bug has been marked as a duplicate of 5618 ***