I have only just seen this, but the following worked for me and may be useful to anyone else having the same problem. I went from Mandrake 8.2 to 10.0 Official. It seems to work best if you do an install rather than an upgrade, and do a minimal install. The original problem in my case seemed to be something to do with SCSI drivers.
1. Copy the whole of CD 1 to your hard disk (you need to have a working system already).
2. Make a floppy using hd_grub.img on CD 1.
3. Go to
http://qa.mandrakesoft.com/hd_grub.cgi and follow the instructions. When told to copy the file to a floppy, use the one you have just created.
4. Boot from the floppy.
5. Follow the onscreen instructions. When prompted, enter the path where you put the copy of CD 1.
When you have finished, put CD 1 into the drive and enter the following as root, to make all of the CDs available:
urpmi.addmedia --distrib removable://mnt/cdrom
One more oddity - soft reboots do not work after installing as above (hard reboots do). The system hangs after the message "Uncompressing Linux... Ok, booting the kernel.". I don't know what causes this, but it is not a serious problem because pressing reset at this point boots normally.