Hi Cainus,
I am no expert on raid atall so someone else might be better to help you in this matter,
However I will tell u as much as I can.
As far as I know there are two kinds of raid. Software raid and hardware raid.
Hardware raid needs a special motherboard which is compattable with raid or else a raid-card (Like a graphics card).
To setup hardware raid (So to choose which disk gets mirrored with what) you have to go trough the bios or some kind of bootable media. (Since it has to be set up before anything is installed on either hdd.)
Now here is the part which I dont know and where your problem lies; what to do if one of your hdd's breaks down and you want to re-complete your raid array with a new hdd? I think there should be a solution but I sure havent found it yet, I would say there is some way to 'restore raid-array' since else the entire point of raid 1 would be useless. However I do think its very possible that this 'restore raid-array' option is only useable when you use the same hardware, which isnt possible in your case.
Anyways, my solution for this previous problem turned out to be software raid.
Software raid is setup completely different then hardware raid, it doesnt need a compattible motherboard or raid-card and can be setup trough the operating system. Therefore you have to have an OS installed before you can set it up, which meens you have to have data on atleast one hdd and that meens you can keep one hdd intact. (The other one does need to be empty)
How to exactly turn on software raid is described in my other post. Just remember whenever there are two solutions to a problem there also are diffrent pro's and con's just like hardware and software raid.
If you use software raid you have to change your hdd to 'dynamic' in doing so most image programs like ghost and acronis wont recognise it anymore and wont be able to restore an image.
Also they say that hardware raid is more reliable then software raid, but then again they also say that overclocking is a bad idea
I hope this helped you and I am sorry I cant give you any more information on your specific problem.