You don't tell us what exact SATA RAID chip or card you intend to use. A few SATA RAID offerings are indeed true RAID setups but most use on-chip RAID software to emulate a hardware RAID. Examples of the latter include the very common sil3112 and Intel CHR-5 chips (often included on the motherboard on current motherboards).
Three links you probably want to read before purchasing a sil3112 or intel CHR-5 based board:
Using software RAID in Linux can often get as good performance results as when using these quasi-RAID chips, so I think you should consider that. Also, there are no hard drives that can single-handedly saturate a UATA-133 channel at this time, so going with software RAID and a well supported ATA controller is often more easy and provides equal or even better performance. Also consider getting an external ATA RAID card - several card manufacturers provide documentation so the drivers are available in the Linux kernel already.