Windows Server 2003 provides support for volume mirroring.  To get this set up correctly, you need at least two physical disks.

• The first disk (I'll call it "disk0") must be a dynamic disk.
• The second disk (I'll call it "disk1") must be a dynamic disk.
• Disk1 must have unallocated space at least the size of the volume you intend to mirror.

Seems simple enough.  However, when I opened the Disk Management MMC snapin, clicked "Add Mirror" on disk0, and chose disk1 as the target, I got this error message:

Cannot mirror to a disk with a different partition style.

Both disks were marked as "dynamic," so I wasn't sure what Windows was complaining about.  But when I right clicked on disk1, I was able to convert the disk from dynamic to MBR.  After making this choice, it worked.  Moral:  there's more to the label "dynamic" than meets the eye.