Which would be faster, two SATA I drives running on a Raid 1 system or a single SATA II drive?

-Dman

RAID 1 is meant to safer, not faster. Theoretically reading could be faster, but as far as I know even that isn't always the case.
RAID 0 on the other hand is meant to be faster (but less safe).
As for speed, my guess is that a RAID 0 configuration would be fastest, I doubt current hard disks are fast enough for the connection to be the bottle-neck, but I could be wrong.
There are other forms of RAID btw. The most popular alternative is RAID 5, which isn't very fast (at least not when writing), but is safer than RAID 0, while being more flexible than RAID 1. Basically RAID 5 spreads data over a few (at least 3) hard disks, but uses one of those for redundancy (so when one drive fails it can be replaced without data loss). I'd suggest Googling for more information if you're interested in RAID.

Are Serial ATA II drives on the market? I did not see any. I have a Raid 0 setup with two Seagate Barracuda SATA drives and it is very fast. I didn't make tests ( like sisoft sandra or hdtach) yet, but I expect transfer rates about 100MB/s. Big improvment is noticeable when big files are copied ( movies, lossless musis, archives ). All system is more responsible too...
As Jasper mentioned, Raid 0 isn't safe so regular backup is a must.

You're not going to benefit much from a faster data link. The limiting factors are really disk rpm and seek time. For speed, you should use RAID 0 (striping).

If you've got one of the newer Intel chipsets (915/925), you might want to try the matrix RAID feature. You can segment each drive in the array, and do RAID 0 on one set and RAID 1 (mirroring) on the other.

EDIT: grammatical error.

for speed, a Raptor II (I don't think they are SATA II, but do support NCQ).
RAID 0 only if you back up often, and it also doesn't help with seek times, just transfer rates.

I assume you are referring to the 74GB Raptor, correct? If yes, the Raptor only supports Tagged Command Queuing (TCQ) not Native Command Queuing (NCQ). Tests at Storage Review have shown that TCQ has no benefits for single users (and I believe is rarely implemented on chips). NCQ does have some benefits for single users but only in certain circumstances (when the drive is being accessed by mutiple sources. Regardless it is nonetheless a damn fast drive.