It will be RAID 1, preferably the same hard drive sizes.
You can do it in Windows or if your motherboard supports it, onboard RAID.
1. Make sure you have no data on 2nd harddisk.
2. Go to start - right click computer and select manage
3. Select disk management
4. Right click ( where it says Disk 0, Disk 1 ) and convert each disk to Dynamic Disk
5. Create Mirror (right clicking the partitions and select "Add mirror" on to disk 1, then do the same with the C:\ partition.
Using the On-board RAID is a bit trickier.