You can not create a RAID1 without destroying the RAID0, You have to create a RAID0 with the new drives. Then you can use a program like Norton Ghost or Acronis to clone the disk.
You will have to fix the boot record on the new RAID and set it to boot in the BIOS.
I have seen people use system backup and restore to move the OS. Goto Control Panel > Backup and Restore > Create a system image. To the new RAID0 and then use disk management to expand the drive size to use all the available space.