OK it works!

The timer doesn't change so you have to time it manually, took about 40 minutes for the 160gb hard disk I was using.
Follow the instructions on the above post's weblink, it doesn't seem to work if you just try to disable the passwoed? I had to do the erase bit as well.
Then formated on a PC, all ok.
I used a DVD disc not a usb drive, and I haven't tested HDAT2 with XBOX drives. You will still need to know the lock pasword
Hope this info is useful to people

http://www.theoriginalxboxshoppe.weebly.com
http://www.ebid.net/uk/stores/Computers-and-Consoles
Crystal Xbox v1.4, Xecuter 3, 500gb sata hard disk, 1ghz CPU, 128mb RAM, HD component 720p, blue LED's.
Crystal Xbox v1.4, Xecuter 3, 320gb sata hard disk, stock CPU, 128mb RAM, HD component 720p.