I should know better than to wade into this mess, but I am a "computer guy", professionally for almost 20 years. So here goes...
RAID 0 writes exactly the same data to each drive in a pair of drives, so write speed is exactly the same as a single drive. But reading from the drives is independent, so read speed is theoretically doubled. "Theoretically" meaning that if the transfer bus can handle it and the controller has sufficient buffer RAM, you get doubled read performance.
In Photoshop terms, if you're batch processing a set of RAW captures into some other format, how much of the total time is spent reading from and writing to the drive(s)? As the resulting file size increases in relation to the source file size the benefit of RAID 0 fades into obscurity... remember: reading is faster, writing is unchanged. So if you're reading 20 MB files and generating 20MB files the RAID 0 setup will take AT LEAST 75% of the time the single drive setup will take (read time is 50% of total time, write time is 50% of total time, RAID 0 read performance exactly double). If you're reading 20 MB files and generating 80 MB files, the RAID 0 setup will take AT LEAST 90% of the time the single drive setup will take (read time is 20% of total time, write time is 80% of total time, RAID 0 read performance exactly double).
But then we get into how long does it take to write X bytes versus read them? On most drives, writing takes more than twice as long because the drive itself writes the data and then reads it back to verify it's correct. So then the above examples become even worse.
Out here in the real world, processing time ain't zero, either... far from it. The first example (20MB in, 20 MB out) may really be 25% read time, 50% processing time, then 25% write time. So then the total time of RAID 0 versus single drive becomes almost 90%. The second example (20 MB in, 80 MB out) may really be 10% read time, 60% processing time, and 30% write time. The total time of RAID 0 versus single drive becomes 95%.
So RAID 0 is really only applicable to applications that read a lot and write very little. Databases are the classic example - most are searched endlessly but updated only rarely. Photoshop, at least in my use, writes more than it reads. Bridge building thumbnails will be much faster, but not most of the workhorse functions, with a RAID 0 setup.
Conclusion: RAID 0 offers little benefit for Photoshop. Buy a faster single drive. Use separate drives for operating system, data, and scratch. Use the fastest transfer bus available: SCSI320 or FireWire.
I personally use 15,000 rpm SCSI internal and FireWire external drives in a Dell Precision Workstation 340 with a 2.4 GHz Pentium 4 processor with 1 GB of RAM (2002 vintage). For my raw captures from a Canon Rebel XT, 1 GB of RAM running Windows 2000 has proved to be plenty, and I work in ProPhoto RGB.
And now back to your regularly scheduled photographic content...