A) I don't see any point in setting up a RAID on a single disk. RAID 0 improves performance over *multiple* disks. RAIDing the partitions on a single disk will actually hurt performance. mdadm might actually be confused as to why in the world you're RAIDing partitions on the same disk, and that could be causing the error.
B) You need to make the partitions to be RAIDed a Linux RAID filesystem ('fd' in fdisk).
C) RAIDed partitions should (and I can't emphasize that enough) be the same size. You are RAIDing partitions that are different sizes by a factor of 100.
D) The array might very well have been created after the first try, just without the disks you wanted. At that point you'd need to stop the array and get rid of it.
E) Grab
Webmin. It lets you do the whole thing from a nice web-based GUI, making the process a great deal simpler.