You can't set up a RAID 0 with just a single drive so I'm not sure what you did. Is this going to be a boot drive? If so, the array needs set up before the OS is installed.
1. Go into the raid bios to setup and configure the raid. This will allow you to pick which drives to include in the array and wether to mark it bootable or not.
2. Install the OS. The array should appears as a single drive at this point. If you set up raid 0, you should see a 1Tb (2x 500Gb) drive. If you set up a raid 1, you should see just a single 500gb drive.
3. If this is XP, you will need to use the "F6 add additional drivers" to install the raid drivers during the install process. Unfortunately, XP only allows installation of additional drives from a floppy drive.