If you want to know how Grub calls your disks just invoke a Grub prompt and use the "geometry" command. Say you want to know the 1st and 2nd disk just type
By looking at the partitions you can be sure your disk order from the mouth of the horse (Grub in this case).
Grub names the disks exactly in the order handed down by the Bios.
If you have only two disk hda and hde ( In Linux convention ) It will still be named (hd0) and (hd1) in Grub. You must have hdb and hdc hooked to the CD and DVD rom.
Also inside every Grub installation there should be a file /boot/grub/device.map that maps the disks order. You can take a look there too.
pljvaldez has spelled the multi booting the easy way, by chainloading. That is an universal method (exactly the way Linux boots every Windows) for booting any PC system.
The last link of my signature has a range of booting tips I have collected and summarised.