We had an interesting situation come up recently.
When we slaved up a failing WD hard drive to our data mule machine running Windows XP Pro SP2, we were not able to cancel out the default disk scan Windows wants to run on the WD.
We had to reboot the system a number of times due to the poor condition of the drive.
The only way we could bypass the scan was to have a PS/2 keyboard plugged in so we could hit the "any key". Right at that point, Windows had disconnected the USB and thus the USB keyboard.
We have seen this on servers as well right at the 34 minute mark of a Windows Server 2003, 2003 SP1, and 2003 R2 install. The USB would get knocked out, and the system would ask for the RAID driver to be accepted right after it. With no PS/2 keyboard, we would have been stuck. The same would be true for the Disk 1 install of SBS.
Microsoft Small Business Specialists