If your root partition is the 1st partition on the 2nd drive then something like this will work.
SATA Drives
title Slackware64 13.0 (/dev/sdb1)
root (hd1,0)
kernel /boot/vmlinuz root=/dev/sda1 ro vga=normal
IDE Drives
title Slackware64 13.0 (/dev/hdb1)
root (hd1,0)
kernel /boot/vmlinuz root=/dev/hda1 ro vga=normal
Here's my menu.lst
# GRUB configuration file '/boot/grub/menu.lst'.
# generated by 'grubconfig'. Sat May 16 15:33:42 2009
#
# The backup copy of the MBR for drive '/dev/sda' is
# here '/boot/grub/mbr.sda.7789'. You can restore it like this.
# dd if=mbr.sda.7789 of=/dev/sda bs=512 count=1
#
# Start GRUB global section
timeout 10
default 0
color light-gray/blue black/light-gray
# End GRUB global section
# Linux bootable partition config begins
title Slackware64-Current (/dev/sda5)
root (hd0,4)
kernel /boot/vmlinuz root=/dev/sda5 ro vga=normal
# Linux bootable partition config ends
# Linux bootable partition config begins
title Bluewhite64Current (/dev/sda6)
root (hd0,5)
kernel /boot/vmlinuz root=/dev/sda6 ro vga=normal
# Linux bootable partition config ends
# Linux bootable partition config begins
title Slamd 12.2 (/dev/sda7)
root (hd0,6)
kernel /boot/vmlinuz root=/dev/sda7 ro vga=normal
# Linux bootable partition config ends
# Linux bootable partition config begins
title Bluewhite 12.2 (/dev/sda8)
root (hd0,7)
kernel /boot/vmlinuz root=/dev/sda8 ro vga=normal
# Linux bootable partition config ends
title --- For help press 'c', type: 'help'
root (hd0)
title --- For usage examples, type: 'cat /boot/grub/grub.txt'
root (hd0)
The grub from Slack-Current will boot ext4 partitions.
ftp://slackware.mirrors.tds.net/pub/...nt/extra/grub/
Hope this helps.