Hi Paul, welcome to NeoSmart.
As you've found out the hard way, VistaBootPRO is no longer the good program it used to be, and is now highly unstable, unreliable, and b0rks your PC.
The good news: EasyBCD can fix it
In EasyBCD 1.6 from Vista, delete any and all XP entries.
Create a new XP entry.
AT this point, XP entry will try to boot from the boot drive - the one with the "BOOT" folder, which is most likely the Vista drive. If the Vista drive already has NTLDR and ntdetect.com, well and good. If it doesn't - copy these files to the Vista drive from the XP drive. they're in the root partition.
Now XP should boot - if it doesn't that means that Boot.ini is not configured correctly. Just open the boot.ini file in the Vista drive and modify the partition number from 0 to 1.