I am in total agreement with ugpsobta, make your machine a dual boot.  Poser 7 with Windows XP 64bit is a finicky beast at best.  You will get to enjoy the old popular BSOD on occassions.  I usually pose on the 32 bit side and move to 64bit for rendering.  This allows me to take advantage of my extra memory.  Just understand that you will get somewhat of a speed increase due to any memory you have beyond 3.5 gigs, you will not see a performance enhancement due to the 64 bit OS.