I have to admit that I have not seen any Mac code, but even if you migrate from XP to Win 7, some or the other things go for a toss, OS wise, 32/64 bit (Active X controls), Office 2003-2007 wise VBA functions some not supported.
All these within MS domain, cant think of non-MS ones, but if they are not bent towards macros, it might be easy tossing them over.