My first attempt build a new kernel. I follwed all the advice hereabouts for building and installing the new 2.6 kernel.

But on booting up I get

VFS cannot open root device "sdb1" or unknown - block(0,)
Please append a correct "root"=
Kernel panic - not syncing

The 2.4 kernel is fine if I select it

This is the relevant bit of grub menu.lst

title SlackwareLinux (on /dev/sdb1)
root (hd1,0)
kernel /boot/vmlinuz-custom-2.6.16.9 root=/dev/sdb1 ro
savedefault
boot

title SlackwareLinux-2.4 (on /dev/sdb1)
root (hd1,0)
kernel /boot/vmlinuz root=/dev/sdb1 ro
savedefault
boot

title SlackwareLinux-2.4 (on /dev/sdb1)
root (hd1,0)
kernel /boot/vmlinuz root=/dev/sdb1 ro
savedefault
boot

This is fstab
/dev/sdb2 swap swap defaults 0 0
/dev/sdb1 / ext3 defaults 1 1
/dev/sda2 /mnt/windows ntfs ro 1 0
/dev/sdb3 /mnt/kubuntu ext3 user,noauto 0 0
/dev/sdb5 /mnt/winlin vfat user,umask=0 0 0
/dev/sdb6 /mnt/winback vfat user,umask=0 0 0
/dev/sdc1 /mnt/flash1 vfat user,noauto,umask=0 0 0
/dev/sdd1 /mnt/flash2 vfat user,noauto,umask=0 0 0
/dev/hda /mnt/cdrom iso9660 user,noauto,rw 0 0
/dev/fd0 /mnt/floppy vfat user,noauto 0 0
devpts /dev/pts devpts gid=5,mode=620 0 0
proc /proc proc defaults 0 0

Any ideas?

You need to be sure that the fs for '/' is compiled in the kernel, not as a module.

It is in the kernel.

In fact I just copied over the old .config from the 2.4 tree and the only change I made was to select the opteron processor

CANNOT DO THAT.

Must get/make a config for the 2.6 kernel. Different beasts.

Just "make menuconfig" or "make xconfig", and make a new config file

Sorry. I did not make myself clear. I copied over .config then ran make menuconfig

The other usual cause for this is that you didn't compile in support for your hard disk drive (usually IDE support). Find out what IDE controller you use and make sure it is supported in Device Drivers > ATA/ATAPI/MFM/RLL. Or make sure the generic support is enabled.

Well I have SATA drives. Could that be the problem? SCSI disk support is in. Low level drives are as modules. My 2.4 kernel is the sata.s installlation kernel.

I have a result - of sorts

I added low level NVidia sata support and I have managed to boot to the command line.

The problem now is that the usb keyboard and mouse are not working. I presume this means back to menuconfig?

Yeah, that sounds like you didn't include USB support for Human Interface Devices. It is in the top level of the USB tree.

Thanks to everyone that has helped me with this.

I had two more problems:

Compiling the NVidia driver. Searching LQ revealed that this needed patching.
Lack of sound. I had to compile ALSA into the kernel.

It is now working.

One more question. During this testing phase everytime I wanted to switch from 2.4 to 2.6 I had to re-install the nvidia drivers. Is there anyway of having the two sets co-existing on the system. Installin one lot uninstalls the others.