Sounds like a WinXP driver problem or incompatibility.
I agree. It is a brand-new computer, configured by Polywell. Everything seems to be working great, and I've already burned over twenty DVDs, and when tested using CD-DVD Speed running under Vista, those burns are excellent (although I am testing on the same unit that made the burns, so the results may not be valid).
I've poked around all the Device Driver settings for the IDE channel, DMA controller, and of course the drive itself. It's using the original Windows XP driver (dated 2001). I don't know of anything more recent. I've written to Polywell to see if they have any ideas, but I don't expect to get very far with that, since the unit is performing its main function just fine.
But since it works under Vista and not under XP, and since others have the same unit and it works under XP, then it must be something to do with either the XP configuration, or the fact that I have all these controllers. I suspect that just as the Nero Infotool got confused (see my earlier post with the screen snap), CD-DVD Speed is getting confused by how things get reported by the IDE, SAS, and RAID controllers.