I notice on the Plogue website (home of sforzando) that the plugin requires Windows 7 or better. It's listed at the below link under "Requirements".
https://www.plogue.com/products/sforzando.htmlIf sforzando is not installed, BIAB should default to the the installed softsynth that comes with it.
I'm guessing that your Windows XP is 32-bit. If so, and if I recall correctly, SFZ+ player should let you play PG Music's HiQ sfz sounds.
http://www.hitsquad.com/smm/programs/sfzplus/On my Windows 7 system, the PG Music HiQ sounds are found under...
C:\Program Files\PG Music Inc\Band-in-a-Box Sounds\Programs
I'd imagine that they are installed in a similar location on your computer. SFZ+ could be loaded as a VST for a MIDI Supertrack and then they HiQ sfz soundfont could be loaded into SFZ+
Hopefully some of these thoughts are useful for you.
Regards,
Noel