If it is the ML530 1st generation, then it has a regular Wide Ultra-2 SCSI adapter. If it is an ML530 G2, then it should have an Ultra-3, but neither one supports hardware RAID.
So if you rebuild the mirror through disk administrator as manicmog suggested, you should be fine.
One thing to keep in mind, though, is that if you boot from the software-based mirror and the primary drive fails, Win2k sometimes can have a problem booting to that secondary drive. The data will all be there, but you can have boot issues. So the best practice for software mirroring would be to boot to a stand-alone drive, and put all of your critical data on the mirror.