1. Your RAID 0 array is working if the OS reports the RAID 0 volume as a single 279GB drive.
2. RAID 1 (mirror) is what you would need for the array to be seen as a single 140GB drive, but since you appear to want a striped array, you have it set correctly.
3. To test whether your RAID 0 array is actually operating correctly, run a benchmark with HDTach
. Take a screenshot of the results, upload to an image hosting page and post the link here.
4. You may want to brush up on what RAID is and how it operates. Great article on Wikipedia: http://en.wikipedia.org/wiki/RAID