Here is the situation:
----------------------
Current install: RH 5.2
Upgrading to:    RH 6.1
Condensed /etc/fstab content:
  /dev/sda1  /     etx2  defaults 1 1
  /dev/sda2  /usr  etx2  defaults,usrquota,grpquota 1 2
  /dev/sda4  /var  etx2  defaults,usrquota,grpquota 1 2

When I upgrade to RH6.1, and choose to upgrade, the installer does:
- find the rpm database
- read the rpm database
- when trying to find packages to upgrade, it dump the stack of the python
  program that caused the crash.

Solution:
---------
I booted the old RH5.2 and edited the /etc/fstab and remove the quota
options. The above fstab becomes:
  /dev/sda1  /     etx2  defaults 1 1
  /dev/sda2  /usr  etx2  defaults 1 2
  /dev/sda4  /var  etx2  defaults 1 2

Then I try to upgrade and It did find the package to upgrade.

Reproduction:
-------------
Then I want to confirm the BUG. So I cancel the upgrade, then boot
again RH5.2 and restore the original /etc/fstab.
Then I try o upgrade, doing exactly the same procedure and it failed again.
So, this is a reproducible BUG.

The python stack:
-----------------
When the installer show the stack, I choice "debug" and then enter
in the Pdb. In the Pdb I run the command "w" to see the stack, and
here it is (textually):
---------------------------------------------------------------------
(Pdb) w
   /usr/bin/anaconda(235)?()
-> pdb.post_morten(tb)
   /usr/lib/python1.5/site-packages/text.py(1000) run()
-> rc=apply(step[1](), step[2])
   /usr/lib/python1.5/site-packages/text.py(251) __call__()
-> todo.upgradeFindPackages(root)
 > /usr/lib/python1.5/site-packages/todo.py(1155) upgradeFindPackages()
-> packages=rpm.findUpgradeSet(self.hdList.hdlist, self.instPath)
---------------------------------------------------------------------

Procedure in the Installer:
---------------------------
- when booting from the CDROM, type "text" in the lilo prompt
- Press Enter at the welcome
- Select upgrade
- select English language
- select US keyboard
- (I think thats is all)

Instalation media:
------------------
CD buyed in cheapbytes.com
The CD is the CD image available in the ftp of RedHat.

Hope this help
Oliver