If they won't answer pre-sales questions like yours, how will they treat after you parted with the money?

As to RAID 0 it's a gamer thing. It's certainly less safe than one drive and yes, you need 2 to make a RAID 0 array.

More at http://reviews.cnet.com/4520-6029_7-5884226-1.html

I recommend the drives Gateway puts in the machine. Otherwise there will be finger pointing when it fails.