I have figured it out somehow
. When I setup RAID 0 with 2xHDs of 160
GB, during Vista Setup, it will still show 2 partitions. So, to really
make one drive out of 2, I needed to remove the 2nd partition of 160GB
and expand the first one to 320GB and then it started to look like one
drive which was my goal.
So when creating RAID 0, my mistake was that I thought that Vista Setup
saw 2 disks while it actually saw 1 disk with 2 partitions (that are in
reality 2 disks). I had to manually remove one partition and extend
another to make it look like 1 disk.
I hope it makes sence the way I described it.
have a nice day