RH 6.1 does not support harddisks with more than 65535 physical cylinders.
On such disks (e.g. the IBM Deskstar 34GXP), the installer complains about
not begin able to read the partition table on the disk. Fdisk says 'cannot
open /dev/hda' or something similar. The kernel does report the correct
size and partition layout in the boot messages.

The cause appears to be a flaw in the kernel, which uses a 16-bit field to
store the cylinder count. Patches are available, reference
http://www.win.tue.nl/math/dw/personalpages/aeb/linux/Large-Disk-12.html

It should be sufficient to provide a new boot disk with a patched kernel
(provided the installer can be made to copy the kernel from the boot disk
instead of the CD). Hopefully, this problem will be resolved sooner rather
than later!