Hi,
In my case i had the same problem, migrate from non RAID to RAID in windows 2003 server and DELL POwerEdge 1800 and i made the following procedure:
1 - Keep the hard disk in the non raid controller and install the raid controller borad in the server.
2 - Boot the windows 2003 server. windows will find the new controller (with no disk at this time), and will install all needed drivers for this new RAID controller.
3 - After windows make all drivers installation i had made a image file using Norton Ghost 2003 (boot with norton Ghost disk and burn a set of DVDs with the hard drive image file.
4 - Install the new disks in the raid controller and create the arrays and initialize it.
5 - Using the Norton Ghost image file, restore thte image in the new array created in the RAID controller.
6 - Start windows and new hardware will be installed and windows will ask for a reboot.
7 - New RAID system is installed and operational.
Please note that this procedure work for me with no problems, and still working without any problems.
Sorry for my poor English, i am from Rio de Janeiro, Brazil and i am posting this information just to help you and other in sharing information,
Best Regards for all
Marcos Silva