genuine advantage

OK, I have 4 (four) LEGITIMATE copies of windows XP on CD.  I only have 2 computers with windows XP installed.  I want to see of one of my other computers would work with Vista.  But, vista upgrade adviser won't work without running windows genuine advantage... and my Extra legit copies of windows won't work... they won't let me install them because they were installed before...  I know I can probably call M$ to transfer a license but I just want to see if the damn box will work with vista so I can use it as a media center pc through my xbox 360 to my TV. 

What a pain in the ass.