Although there are probably some laptops that are unrepairable, because the specially designed parts are no longer available, I appreciate your comment that there are no non-repairable desktop computers. I think you're also right -- I should mention CompUSA by name, since they screwed this up. No point in being dainty about it. It was really maddening to have them make this absurd statement repeatedly, directly. One approach might have been to have a sufficient tantrum that they would have given me my money back right then, but that's not my style. In going after them, my next step will be a certified letter, beginning "I am typing this letter with the computer you said was unrepairable." It is premature to assume they're going to get off lightly.
My tech tried my old motherboard w/ an old 133mhz bus Duron he had, before applying the BIOS upgrade to speed up the bus to take a 333mhz XP. So, no, he didn't fry my new CPU. It's working fine.
The story of two drives is a little more complex. My old 2nd drive was weird -- 2nd tech. concluded some minor damage to the internal controller ("minor" in the sense that it wasn't just totally dead). As mentioned, it was interfering w/ the system during reinstall. Some files could be accessed, but could not write to it and files became increasingly unavailable. Fortunately, there was nothing I needed on the 2nd drive, since I used it solely for backups.
My old drive #1 was working fine. My 2nd tech made a full Ghost backup of it, just to be careful, for which I'm grateful. I think it was just more serial bad luck that it then physically broke (clunk, clunk) before he could get the system back to me. Or, maybe it was good luck. If he'd reinstalled the OS on my old drive #1 & given it back to me as a working system, he'd probably have erased his Ghost backup and then when my drive #1 crashed I'd have lost everything because my backups were on drive #2.
As to the RAM, yes, it was replaced and it's the RAM that is now working fine. (Extraneous details: while the computer was at CompUSA & I was told it needed a new CPU & MB, I got the KV7 & an XP 3200, to use the 'new' 400 mhz bus. So, I got 512 mb. of 400mhz DRAM. When tech #2 was trying to get the KD7 to work, I got an Athlon 2700 instead since the KD7 couldn't take the Athlon 3200. So, when tech #2 moved on to the KV7, it was too late to get a refund on the Athlon 2700 so I'm only using 333 mhz bus speed. I thought "OK, I'll end up w/ 1gb of RAM, using my old 512 mb 333mhz stick and new 512mb 400 mhz stick." Tech #2 found that either stick would work, but they wouldn't work together. So, I've sold my old 333mhz stick.)
You also mentioned the problem w/ AMD. It was the AMD fan that failed, despite the 3 year warranty. At best, I'd get a new, old processor from them. If I get time, I may submit the claim, and sell whatever processor they send me. I had a problem before with the AMD, which turned out to be incompatible w/ one family of video cards (a fact they'd failed to mention). I stayed w/ the AMD originally in the hope it'd be compatible enought that I'd not have to reinstall all my software & peripherals. That didn't work out, obviously, but it seemed like a good idea at the time. Next time I'll take your suggestion and go with Intel.