I am experiencing all the same problems a described in this thread. The HD boots fine to a regular dos prompt in the WP, but after starting the install and allowing WIN to copy all it files, when it comes to the first reboot in the install process, it goes through the usual BIOS checks, recognises the Hard drive OK and then as soon as it goes to the HD to start Windows, it hangs with the cursor blinking in the left hand top of the screen - and goes no further. I have taken the drive out and reinserted it in my desktop and the drive is readable and bootable from there. The BIOS settings on the WP fit what everyone says to do.
I too have trawled through this terrific forum without finding any solution to this problem
However I did find and follow up on one thread regarding making the DOC the first drive in the sequence and booting from that. Having achieved the initial DOS prompt on the HD, I took advantage of this to use Hackwp (available elsewhere on this site) to load a Win98 image onto the DOC. Afterwards by disabling the IDE on the WP the WP then boots fine from this but if you re-enable the IDE interface the WP boots from the HD.
I went to the www.m-sys.com site and after much searching downloaded the DOS Tools version 4.2. - its there and difficult to find but you need it because the v5 tools-set does not have the DUPDATE utility. The 3 files needed are DUPDATE.exe DINFO.exe and DOC42.EXB
Run DINFO and check the start address of the DOC - mine was D600. The command line to run is then
DUPDATE /WIN:D600 /S:DOC42.EXB /FIRST
Reboot the machine and it will start from the DOC and the HD shows as the next drive(s) letters and can be fully accessed.
To reposition the DOC back behind the HD in the boot sequence run DUPDATE /WIN:D600 /S:DOC42.EXB and reboot.
DINFO reports the drive letter assigned to the DOC so you can see where it sits in the chain. I couldn't find and any more info on the command line parameters for DUPDATE.
This allows you to run the webplayer using the HD attached for data etc. I tried to load a substantial program that did not allow a choice of where to place temp files but there was not enough space on c: (theDOC) to hold the temporary files. If anyone knows how to uncompress the files on the DOC and move them to the HD and leave just the minimal boot files on the DOC, that would be great.
This still does not find the real solution of how to make all HDs boot and reading this forum I think many others are frustrated by this.