nForce3 SATA controller - grub hangs

[Barry Jackson]

Hello,
I have a dedicated grub (NOT grub2) partition from which I chainload 
into various Linux systems on two (non RAID) SATA hard drives.
Everything works perfectly using a Silicon Image PCI SATA controller 
card for both drives :-
Silicon Image, Inc. SiI 3512 [SATALink/SATARaid] Serial ATA Controller 
(rev 01)
However, if I try to use the on-board SATA controllers :-
nVidia Corporation nForce3 Serial ATA Controller (rev a2)
then however I try to boot using grub I hit problems.
Using a grub boot floppy or a CD with :-
find /boot/grub/stage1
finds only the installation on (hd0,4) - after which grub crashes.
Total lock up - only CTRL/ALT/DEL can get out of it.
The same happens using tab completion with "root ("
With the Silicon Image controllers I can boot anything manually from the 
grub prompt or from my grub partition menu.lst.
The system on (hd0,4) does boot and run using the nforce3 card, and all 
the partitions on all drives are accessible using the sata_nv driver in 
that Mandriva 2009.0 installation.
Is this a grub bug ? ...or is this a problem with the nforce3 
controllers? .. or something else?
TIA,
Barry

Full hardware set-up (lshw output and fdisk -l) is here:-
http://barjac.pastebin.com/PPi5Yzeg