I've heard that the systemboard bios on some of those machines will completely hide the diagnostic partition from being seen no matter what OS you use. Best bet is to move the drive to another system (preferably a whitebox, or at least a non-compaq) and clear out the Partition Table, MBR and first 50 or so MB of the drive (If you don't care about any of the data on it that is!)
actually, that was one of the first things that I tried, but even in another computer Partition Magic 8 didn't see it and would make any changes to the partition it did see because it reported the error and advised I backup the data, remove everything and start over.
The solution, of course, is the wipe the drive and restore the primary partition from an image file but I can't find anything that will image it .... Acronis and Drive Image report a partition error. I could go through the hassle of wiping the drive and starting from scratch, but I would really prefer avoiding that.