I am trying to configure grub to be able to boot from any of the four hard-drives that I have, three of which are plugged into an nVidia RAID controller and the other is plugged into a JMicron controller. Grub seems to only see the loan one and not the other three. Is there a way to get Grub to see the disks attached to another controller?

The ones plugged into the nvidia raid controller are not visible? Is this controller capable of acting like a regular sata controller, or is it a built-in fake-raid?

fdisk -l
provides a list of drives the kernel can see.

lspci - to check what the controller looks like to linux. Also check your bios to see how it is set up.

If Grub can see one of them, then you can have Grub on that drive and boot the others from there.

I have two Sata drives that I can't boot directly from, I think it's because they belong to another CPU (I'm borrowing my friends CPU and although I've managed to get the raid sorted, so they work, they're not recognized when booting up). My temporary fix is to have Grub on a USB stick and to boot them indirectly.

Reading this back, it doesn't quite sound like the same situation your in, but if you have Grub working, next time you boot, exit to the Grub prompt and type and press Tab I've found this won't work from within the OS, only from the Grub prompt at boot-up time. It should list all that it can see. How are you trying to get Grub to see the drives?

It is built-in fake-raid.

Well there you go - linux will need special drivers to access the raided drives. IIRC dmraid supports nvidia software raid controllers.

http://linux-ata.org/faq-sata-raid.html
http://www.nvnews.net/vbulletin/showthread.php?t=66344
http://www.linuxmanpages.com/man8/dmraid.8.php