error message "cannot verify digital signature of ntoskrnl.exe"

I have installed Vista on drive 0 and it boots up and works
fine. I have XP on drive 1 in partition 1 and it will boot up and work fine
IF I use this drive as the only drive by unhooking the IDE cable from the
Vista drive, changing the BIOS, etc. I have read many of the posts in this
forum but have not seen the ". I have copied the three files from XP to
Vista C: drive : boot.ini, ntldr, and ntdetect.com.
The boot.ini shows the XP to be on drive 1 partition 1.
I have used VistaBootPro to set up for the dual boot from
withjin Vista. The boot choices do show up at boot but the choice for XP
always leads to the error message above.


Any thoughts appreciated.

Paul