Well, there's good news and bad news. The bad news is that I've never had the need to use RAID so I can't help you out there. The good news is twofold:
1. RAID works on linux and has done since the 1990s (RAID is a UNIX construct, after all).
2. GRUB is a bootloader. Like any bootloader, its execution precedes the loading of a kernel. Therefore, the GRUB error you are experiencing technically has nothing to do with your linux install as it has not even been loaded yet. The error you are getting is probably due to the MBR pointing to the wrong partition. GRUB is a 3 stage process. Stage 1 is the MBR code. Its sole purpose is to read the read the Partition Table, find the CHS address of the Bootable partition and go to that address and load the Volume Boot Record (VBR) located there. The VBR points to the CHS address of an image that becomes the second stage of GRUB. That image is, for historical reasons, called Stage 1.5. Stage 1.5 simply contains code about the type of filesystem used on the partition (remember we haven't loaded a kernel yet so the PC has very little idea about where it is and what it's doing). Once Stage 1.5 has been read the third stage (Stage 2) is loaded. Stage 2 is what most people think of as GRUB - the text menu that allows you to choose the OS you want to load. Each entry in the menu is taken from the menu.lst configuration file which contains the filename of and path to the kernel image. Once a menu has been selected, that kernel is loaded and it takes control eventually resulting in your desktop. So there you have it: a simplified version of the GRUB boot process. You should now have some clues as to what has gone wrong with your install, viz. it's probably pointing to the wrong harddrive and/or partition.
To fix things, just wait until the error times out and drops you into the GRUB command line. At the prompt run
It should report back with something like (hdx,y) where x and y are numbers, eg. (hd0,1). You then need to run
substituting your result for x and y. Then run
again, substituting your result for x. This should now have fixed things so you just need to reboot.