OK, to try and explain a bit more clearly.
Mirrored drives are a feature of a RAID Array.
The point being you have an array of multiple HD's of duplicate size etc and with the help of RAID drivers (either via plug in hardware or motherboard software) you can choose utilise these drives in a way that provides extra system redundancy. In your case - you have 2 drives, 1 of which is configured to mirror the other.
As always with drives, the BIOS is where the full picture is found, and if your RAID system is software based there is a good chance it will be shown in the BIOS and that is where you will see the mirrored drive.
You do not need to make any changes - do not fiddle with some thing that is working. Have a look to see what RAID drivers you have but you do not need to do anything else in that area.
If one HD is configured to mirror another HD, it will mirror the drive exactly - so that if your main HD has been partitioned to contain 2 separate virtual drives (C and D) then the mirrored drive will also contain that formatting.
This is all done by the computer BIOS and RAID drivers and Windows does not really get involved at all.
Where Windows gets involved is at the boot process. If the original drive fails Windows has to know that you have a mirrored drive and to bring about a swap to the mirrored drive either by rebooting your machine or seamlessly swapping over to it without your knowledge. In either case you would get a warning telling you your primary drive has failed, as would you get a warning telling you your mirrored drive has failed as well.
Hence the statement that you need to check that Windows 7 recognises your RAID drivers.
I hope that helps a bit.
If you read the additonal blurb on the BBC web site it also tells you to stick with it because swapping browsers on a whim could cause more damage than sticking with the known weak spot. As you are building a new machine - what are the potential hackers (who have probably never heard of you
) going to do? Wipe out your installation of Photoshop or Office on your new computer? Hardly a disaster at this stage!