Fedora 8 system won't upgrade to Fedora 10

[Langdon Stevenson]

I have a Fedora 8 server that I want to upgrade to Fedora 10.  I 
recently did this same task with a workstation and had no problem 
upgrading from 8 to 10 using a DVD.  Just ran the installer, it detected 
the F8 install (on logical volumes over RAID 5) and did the upgrade.

The server is an old machine, so doesn't have a DVD drive.  Therefore I 
am trying to do an upgrade from a DVD ISO image of F10 mounted on 
another server on the network.

I boot the server with an F10 boot disk, choose Install or Upgrade, then 
the installer goes to work, downloads stage 2 from the network.  The six 
disks in the server all run for a while, then the installer tries to do 
a clean install.  It does not present the option to upgrade.

I am assuming that the installer can't detect the existing 
installation/partitions (boot and swap are RAID 1, root is a logical 
volume on RAID 5).

Can anyone suggest how to troubleshoot this issue?

Langdon