Instead of deleting bootxp open it up, go to options & restore your boot.ini backup. Choose option 1 if you have not added an operating system. Then go to my computer\properties\advanced\startup & recovery\settings\edit boot.ini. Your boot.ini needs to look like the above. Remove everything after /fastdetect. Save it. Reboot & the original is back. At Windows Bootxp will still pop up wanting to be installed again. Click cancel till you are ready to use it again.
you'll have to unistall bootxp and other 3rd party programs.
here is what M$ says in its :
Windows XP Service Pack 1 Known Issues-Beta Technology Support:
"Customers will receive this message when trying to install SP1 if they have
installed BootXP, Windows Theme applications or other applications that
replace the Windows kernel. This application replaces the NTOSKRNL.EXE
boot file. Customers may see this same behavior with other theme applications
as well such a Windows Blinds and StyleXP.
Uninstall 3rd party theme program from Control Panel > Add/Remove
Programs. Attempt to reinstall the service pack. If SP1 still fails to reinstall
follow steps 4 – 10 in Q327101. Attempt to install the service pack once you
have completed those steps.""
Looks like it might be best to uninstall bootxp & other similar apps.