Here's an update on my thread:
I got the idea today that perhaps Western Digital had a separate driver available for their Firewire external drives, and it might help with my problem. As I searched for available software, I kept running across an interesting point: all the WDC software I found failed to list Vista 64-bit as a supported OS. Some older models don't list Vista at all and even among the XP versions, 64-bit isn't mentioned.
The last time I spoke with WDC Tech Support, they mentioned that even their factory-designed Firewire external drives are experiencing problems with Vista and 64-bit OS's. I have also heard this complaint on other Vista user forums.
So now I am speculating that WDC hard drives are not entirely compatible with Vista and 64-bit OS's and the standard 6.0.6001.18000 disk driver that comes with Windows Vista. And I don't believe WDC intends to do anything about it....the market segment of Vista 64-bit users is probably considered too small to warrant the effort.
Once again I am speculating, but I think Microsoft knows about this problem and also considers the 64-bit market too small to bother with. And I should mention that XP SP3 intorduced some new Firewire and external HDD incompatibilities. So Microsoft's skirts aren't exactly clean on this issue either.
However, MS Tech Support has been working with me on this problem and as of yesterday they offered me a free Vista 32-bit installation disk and free phone support.
This is an unexpected bonus because I purchased an HP computer with Vista pre-installed. MS does not offer free phone support for an OEM installation.....it was supposed to come from the OEM. Through frustrating and persistent effort I found HP free Tech Support is ill-equipped to deal with anything except basic Vista troubles. To get to any higher level tech people you need to pay whether or not your problem is solved. (Based on customer after sales support I expect I've bought my first and last HP computer.)
The explanation for the lack of free phone support from MS is that MS has no control over what an OEM does with their versions of the OS. That's also why they leave it up to the OEM to provide support. But God only knows what HP did with it on various models....even their Tech Support doesn't seem to know (or admit they know).
Here's an example: when I installed my HP All-In-One Office Deskjet printer, I could not get duplex printing to work. HP Tech Support essentially told me that duplex printing was not supported by Vista. This turned out to be anything but true......it was two simple issues, both easily resolvable. It turned out that to select duplex printing the user has to be signed in as administrator (I thought I was and this is part of my Vista learning curve)....presto, duplex printing available. The second issue was that the printing on the back of the page was upside down and the toggle for this was inoperative. It is an HP driver problem and the new driver was available on HP Users Forums for free. But HP seems to be clueless about this and is simply blowing its customers off by making this oversight a (false) Microsoft problem. I was not even referred to the Users Forum, I was left to find this on my own.
So while I still haven't solved the HDD Firewire troubles yet, here's what I've learned: Microsoft customer support has been very good...Western Digital has been poor and HP support thas been very poor. Lastly, Vista 64-bit is simply not worth the trouble for most users.
BTW, through a little bit more searching I've found that PCI Firewire 800 cards with 64-bit Vista support are available and it's my guess that an Oxofrd 912 bridgeboard might also get around the 64-bit issue. But I'm waiting for the 32-bit version of Vista before I spent over $100 for new hardware that might not be needed.
We'll see what happens when I get Vista 32-bit installed.