|What parameters are you passing the hp utility? I haven't done it in a little while but I think it should be:|
HPUSBF X: -FS:FAT -B:"WHERE\COMMAND.COM\AND\IO.SYS\RESIDE"
Usually when you get the 'invalid system disk' and make no changes to the boot devices--such as inserting a bootable floppy--you should get the same error when you hit 'any key' since everything is the same.
Most newer bios' have a "try next boot device" feature, on boot failure it will display the message "Invalid system disk", hitting a key with out changing media will cause it to try the next in boot sequence(if any).