Lets get one thing clear first
You must nominate one Grub in the MBR. I was under the impression that was Mandriva's Grub 0.97. So stick to it.
Issuing grub-install /dev/hdb9 inside Mandriva = ask Grub there to install itself in device partition hdb9. So when you choose to boot to hdb9 Grub boots istelf back!!! It is like two mirrors glued back to back. Whichever way you turn it you only see yourself. Got it?
Now the cure
Since your DSL has been identified in hdb9. The alternative of using grub-install is the Grub shell.
You can invoke the Grub shell in Mandriva and ask the Grub 0.97 to do the leg work for you as follow
If hdb is your 2nd disk then hdb9 is (hd1,8) to Grub, as it counts from 0.
The above commands instruct Mandriva's Grub 0.97 to use the version 0.91 information from (hd1,8) root partition and setup the Grub 0.91 inside it. (I know DSL uses Grub 0.91 and Mandriva uses 0.97 version as I got them both)
grub-install is not as robust as the Grub shell. I usually go for the latter when the first one has difficulties.