It should be a function of the controller you plug it in to, so either your motherboard, or add-on controller card's BIOS. Failing that, I believe XP and higher versions of Windows allow you to create dynamic disks using Disk Management, and you can just dynamically link one drive's contents to a folder on another drive letter.

It isn't easy to simply revert to individual drive operation. The Directory Structure is only stored on one drive. If you wanted to convert to individual disks, you can run any one of the utilities that scans your drive for files and rebuilds your partition tables on the drive that does not have the partition table already on it. It isn't terribly tough, but it is way more work than you will want to do more than once.