How to force os-prober to scan for new hard disk

[Bernard Wu]

Hi Listers,
I just added a new hdd to my dual boot machine.  This new hard disk contains RHEL 5.5 with grub installed in its mbr.
No matter how many times I run update-grub, it doesn't see this hard drive.
However fdisk sees it as /dev/sdc.  How dos I force os-prober to include this new disk when it does its scanning.  I even tried modifying /etc/grub.d/40_custom with this syntax:

menuentry "RedHat Enterprise Linux Server (2.6.18-194.el5)"  {
  set root='(hd2)'
  chainloader +1
}

but when I select it, all it gives me is a blinking cursor and nothing happens.

My current setup:
disk 1 - sda - ubuntu 10.04.2 - grub2 installed in mbr
disk 2 - sdb - win /xp professional - windows in mbr
disk 3 ( new addition ) - sdc - RHEL 5.5 - grub 0.97 installed in mbr

Any advice and suggestion will be much appreciated.

TIA
Bernie