Can I Setup RAID 1 Without loosing my Data?

I have a 1TB secondary hard drive that I store a lot of movies on. I just got a second 1TB hard drive and I want to set the two up in RAID 1 for some data reliability. This is my first try at RAID. Can I do this without having to clear the first 1TB drive? If it helps, I am using Windows 7 RC and my motherboard is Gigabyte GA-MA78GM-US2H 780G AM2+ mATX. Thanks!

I cannot address the question you asked about setting up raid-1, but...

The value of raid-1 for protecting data is that you can recover from a hard drive failure quickly.
It is for servers that can't afford any down time.
Recovery from a hard drive failure is just moments.
Fortunately hard drives do not fail often.
Mean time to failure is claimed to be on the order of 1,000,000 hours.(100 years)
Raid-1 does not protect you from other types of losses such as viruses,
software errors,raid controller failure, operator error, or fire...etc.
For that, you need EXTERNAL backup.
If you have external backup, and can afford some recovery time, then you don't need raid-1.

I would suggest that you install that backup drive in an external enclosure like this:
http://www.newegg.com/Product/Prod [...] 6817173042

Use a backup program like acronis true image home. An extra benefit is that the backup data will be compressed, and empty space is not backed up, giving you the ability to store the backed up data in a fraction of the space.