OK got an answer
I am a 73 yearold one man operation. I simply don't have the resources to migrate/rewrite the program. Windows7 Pro has the 'XP mode' feature, or you can go to a used laptop store and buy a $200 XP laptop. Otherwise, the only program which does the same recursive tax-based math is naviplan extended. The problem is, it is a $1000 hit every year.
I'm not a software guy so any idea how much it would cost to migrate the program?