250GB IDE HD won't boot Vista / Winload.exe corrupt

I am trying to configure an HP Pavilion a6110N (M2N68-LA ASUS OEM motherboard/nForce 430) with an alternate boot configuration by adding a removable WD 250GB IDE drive tray to the system. Motherboard specs here:
http://h10025.www1.hp.com/ewfrf/wc [...] 18&lang=en

For purposes of this discussion my intent was to image the Vista Premium boot partition of my original HP 300GB SATA drive onto the WD 250GB IDE drive, disable the SATA bus in the BIOS, and run with only the IDE activated. The boot partition is only 40GB. I have attempted this process multiple ways, but the end result is always the same: The system will not boot. It fails with a message on a black pre-splash screen indicating Winload.exe is missing or corrupted. The Vista repair process can be run repeatedly and successfully but with no change, i.e. Vista repair says it fixed the problem but upon reboot I get the same or similar message about a different file. I've run up to 10 consecutive repairs with no resolution.

What works:

• Booting from the original SATA drive and formatting/writing/reading/scandisk the 250gb IDE drive. Anything you would normally be able to do with a second HD in this machine works fine. In my mind this eliminates an issue with controller chipset / IDE drivers as well as the HD itself. LBA issues are not applicable to Vista.
• Repeating the above but using a WD 40GB IDE drive resulted in a successful bootable Vista drive. In my mind this eliminates the process of how I get the image on the drive as the source of the problem.
• Repeating the above but using a retail install of XP SP2 on the 250GB drive results in a bootable drive. In my mind this further eliminates the 250gb drive and its boot sector as a source of the problem.

What doesn't work:
All of the attempts below result in the same Winload.exe error message with the 250gb IDE:

• Using an imaging tool to image the working SATA to the IDE.
• Using the HP recovery disk to format and load the boot partition.
• Using a retail install of Vista to format and load the boot partition.

A few weeks ago I also tried a Sabrent low-profile IDE to SATA converter/adapter. I can't remember exactly, but properly jumpered it either ID'd correctly in the BIOS upon POST but was not visible in Vista Device/Disk Manager or the machine hung during POST. I just figured it was incompatible with my on-board SATA chipset. Either way, my experience seems consistent with other users of this type of device. It's just been a very frustrating experience because when you only have one of something and it doesn't work, it's hard to isolate the problem. I've looked at pictures from various mfgs of these low-profile IDE to SATA converters, they all basically look alike, i.e. some OEM in China is making them and they're being branded by Sabrent, Rosewill, etc. Is there any way at all of determining which chipsets are compatible with which devices?

I've even purchased a standard IDE/SATA to eSATA/USB/1394 enclosure and found that a WD SATA drive works fine in it. But when I tested with a borrowed Seagate SATA, my system hung at POST. I'd like to find something like this which would allow me to mount a drive tray in it. But I've also tried an external DVD Writer enclosure but initial testing indicates it won't work with a hard drive.

Any ideas / suggestions appreciated.