Add new hard drive

You need 4 drives for a RAID0+1 array, with 2 drives you can only choose for RAID0 (speed) or RAID1 (reliability). And no you have to backup your data and restore later, because creating a RAID array makes the previous data inaccessible on those drives.

Intel Matrix RAID might be able to do it, i never used it. But that only works if you got an Intel ICHxR (R = RAID support) chipset, like ICH9R or ICH10R. If you have such a chip, go read if it can do what you want. If not you're out of luck.

For this to work, during RAID creation it needs to copy parts of disk1 to disk2. I'm not sure if Intel Storage Manager can do that. I highly advice you to make backups before you actually try anything; if you just setup a raid on the two drives, your data is gone (though still recoverable with tools).