This sounds like you are trying to use a new RAID1 array composed of new 640 GB drives as your boot drive that will be called C:.
The problem is that your OS was installed previously on a non-RAID disk system, and it knows all about how to access such a HDD unit. But no Windows OS knows how to use a RAID array without a driver installed, because RAID systems are not fully standardized. Now, you may have installed the RAID drivers in Windows BEFORE making the clone, but that was not enough. That process will allow Windows to boot from a NON-RAID disk, find out that it should load a RAID driver from that disk and do it, and then use any RAID array it finds. BUT that does not tell Windows that its very first step BEFORE loading itself should be to find and load a RAID driver for the boot drive. So what you have created now is a situation in which Windows starts to load and finds itself trying to use a drive system (RAID1) it does NOT have its own drivers for, so it can't go any further, and it can't find the RAID driver it needs on that disk system it cannot access.
There are four solutions:
1. Install a floppy disk drive in your machine and make two or more copies of a floppy disk containing the RAID driver(s) you need. Keep at least one spare, and keep one in the floppy drive. Every time you boot you will have to push a key (watch the POST screens for the prompt) and tell it to load a driver from the floppy drive before proceeding with the boot-up process.
2. You MIGHT be able to use a USB stick instead of a floppy IF your mobo has a way to make that USB drive look like a floppy to Windows. Or, IF you are using Vista or Win 7 you MAY be able to load the required driver from an optical disk instead of a floppy.
3. You can re-install Windows fresh, using a floppy drive (or optical drive if Vista or Win 7) as the source to load the RAID driver in at the very beginning of the Install process. Then you'd have to re-install all your other stuff, too. Of course, this means you need a full backup of your disk contents now, because a re-Install will wipe your current clones clean. What this Install sequence does is give the first bits of Windows that start the boot-from-disk process a knowledge of where to find and load the RAID driver so it can use the array to boot from, and it's a permanent setup so you don't need the load-from-floppy thing on every boot-up.
4. There MAY be a procedure to accomplish letting windows find the RAID drivers on your RAID1 array (similar to #3 above). I have heard of a process that requires significant editing of the Windows Registry to change the order of loading drivers at the beginning of the boot process, but I don't have a reference to that. If you feel up to the challenge, try searching the web for this information.