Hmmm. According to this there is SLI Multi Monitor support - http://www.slizone.com/object/sli_multi_monitor.html

 

Although it does state Windows Vista 32/64 bit in system requirements. After quickly reading some aged forum threads in various places it doesn't look like Nvidia made drivers to support that for XP unfortunately and I'm not certain about any 'tricks' by the looks of things.