Is it correct in your box that hd0 = /dev/sda ?
It's your first bios drive?
If your paths are right, maybe try:
kernel (hd0,2)/PATH-TO-YOUR-KERNEL ro root=/dev/sda7
One of mine entries (that works) looks like this:
title (hda3) Slackware 11 188.8.131.52
kernel (hd0,2)/boot/vmlinuz-ide-184.108.40.206 ro root=/dev/hda3