Just for the record, not all RAID cards allow you to mix and match drives. My 3Ware RAID cards, which are legitimate hardware RAID cards and not the software based junk mostly discussed here, will *not* allow drives of different types, even if they are the same size.
1. If you lose one drive with RAID 0, everything on both drives is gone. This is why I don't advocate ussing RAID 0 except for non volatile data you can afford to lose.
2. Windows sees the two 80gig drives as a single 160gig drive, at least from a data point of view. You can copy data to and from the RAID drive to a single 160gig drive, which I highly advise doing for back-up reasons.