I would avoid removing anything from the boot manager, via a command prompt! As you know, the bootmgr file, in the root, has nothing to do with XP. The entry may not show in Easybcd or the boot manager. It is not an entry for an OS bootup, but a "leftover" command.. There are definitely remnants of an XP aborted install. The entry will be sitting in a root program "Boot.ini". You could try renaming the Boot.ini, but I am not sure what effect this will have on the overall boot sequence - probably none.
But Mike's suggestion should work. You can also rewrite the MBR, using Easybcd., which should solve the problem, as your computer appears to be still using all, or remnants, of the old OS MBR.
Fwiw, out of interest, do you have any history or knowledge of earlier installs? I am not aware of any entry, for install or setup, which would include the "2003" part.