Connie, thanks**N for this.
The OS got wrecked - somehow. Getting kernel update was done with
yum update kernel
All looked well (other machines rebooted fine with 2.6.9-42 kernel).

For this opteron, trying to boot with the -42 kernel ended up at (my
scribbled notes, might be small numerical errors):

root hd(0,0) ext2fs partition 0x83 root=/dev/sda1  <- the HostRAID RAID1
[Linux-bzImage,setup=0x1400,size=0x195279]
initrd /boot/initrd-2.6.9-42.0.2.ELsmp.img
powernow-K8: init not cpu0
powernow-K8: init not cpu0
mount: error6 mounting ext3
mount: error2 mounting none
switchroot: mount failed: 22
umount /initrd/dev failed: 22

This looks like: 2.6.9-42 can't talk to Adaptec Marvell H2 MV88SX6041
SATA controller, at all.

However after that, trying to reboot back into 2.6.9-11 ALSO failed,
with same errors as above. So somehow ths OS is wrecked.
Fortunately it's not serious as box was due to be rebuilt anyway.

So, have to rebuild it. Broke the HostRAID & will now rebuild it as SL4.1,
having to use the driver aar81xx.rhel4qu1.x86_64.img (have already tried 
SL4.3 but no, that supermicro driver's ONLY for 4.1), with software RAID1.

> If you have either -42 or -42.0.2 installed what does a

See above - can't get there, box does not boot at all with -42 kernel.

> Have you asked SuperMicro when they will have a driver for the SATA in
> question for newer RHEL kernels.  Maybe a src.rpm so that you could make

Have sent a query to them.

> new one as needed.

I don't yet know anything about using a driver .src.rpm. Can someone point 
to simple straightforward howto? Will doing that mean no kernel upgrades 
without a lot of fiddling with recompiling & etc?
What a pity we didn't look into this wretched SATA controller first.

> Make sure you have the latest version of hwdata installed as it has the
> translation table between pci id and driver.

Um, well SL4.1_x86 will install whatever it does & yum update will do
whatever it does. Will those be the correct things?
Will find out, reloading OS now.

Thank you Connie & all the SL crew!