Add another Hard Drive and make it Raid 1 with existing Hard Drive

I want to add another physical hard drive, and configure it to be Raid 1 with an exisiting Hard drive.
  OS is Windows NT 4.0.
  Software Raid.
  SCSI Drives.
  Server: Dell PowerEdge 2400.
We have 3 drives on this server:  2 drives are configured as a Raid Array, and contain the OS.  1 Drive is not configured as raid -- it is F drive.  
 I want to add another hard drive, and then configure it as a mirror of the current F drive,  so we have redundancy for that drive.  So after I'm done, there should be two raid arrays:  The existing raid array that contains the OS, and the new raid array for the F: dirve.   The new drive is the same size as the current F drive.  We would like to use software raid.
Can you please explain how to do this?  (Is it just a matter of inserting the hard drive, and using Disk Administrator to configure the raid, or are there other issues that I must deal with?  I don't want to mess up the existing raid array that contains the OS either, so I'll appreciate any tips about that too.)
Thank you.
GeorgeAsked:
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Lee W, MVPTechnology and Business Process AdvisorCommented:
Do a complete backup first, but yes, it should be that easy - it's been a long time since I setup a RAID, but it SHOULD be that easy.  Do NOT create a partition on the new disk.

Excerpt from:
http://www.comptechdoc.org/os/windows/ntserverguide/ntsfilesystems.html

Disk mirroring - One disk is a mirror copy of the other. This is geared for reliablilty, not speed. The boot and system partition may be mirrored. Mirrored volumes must be of the same size. Mirroring is done by clicking on the volume to be mirrored while holding the CTRL key down, then clicking on some free space of equal or greater size while the CTRL key is held down. Then click "Fault Tolerance", "mirror", and "establish mirror". To break a mirror, click on the mirror, and break.
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tfjeffCommented:
you do not want to use disk administrator to configure raid...you need to use the raid controller or the array manager software.  Please post the model of raid controller your are using and whether or not array manager is installed (if it is installed, please post the version).
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