whats the point, only one device per IDE channel can send or receive data so you wouldn't get any benefit from RAID0. So unless the controller has more than 1 IDE channel (not connector) you're wasting time. Or if you're trying to setup RAID0 and it's not seeing the 2nd drive could be because it's trying to send data to both and they're on the same channel and only one is able to respond before the raid controller times out, in a sense.
As far as the master/slave question, yes you should alway set one drive to master and one to slave. The primary drive, or boot drive, should be master. I think the default is cable select(bases master/slave off where the drive is on the IDE cable) but this doesn't always work.