HOWTO: Boot an existing install

Select "More Options" from the main menu.
Move the cursor to "[EDIT ME] Boot an existing linux install"
Press "e"

At this point you will see the following:
     root   (hd0,0)
     kernel /vmlinuz26 root=/dev/hda3 ro
     initrd /kernel26.img

This needs to be changed to accomodate your hardware.

The first line should be changed to indicate where your boot medium resides.
  "(hd0,0)" is the first partition on the first hard drive (hda1) - change these
  numbers to indicate the partition containing your /boot directory.
  
The second line should be changed to point to your kernel.  If the line above
points to a partition _only_ containing /boot, then /vmlinuz26 is fine.
Otherwise, change this to /boot/vmlinuz.  root= should be changed to match the
partition for your root filesystem.  Other kernel parameters can be added here.