How to share programs between 2 OS?s?

Would anyone know to have a dual-boot-system share programs from the same disk area. What I mean is: instead of installing a program twice, in each OS, I install the program once in one OS. Then just somehow import the settings so I can use the sameprogram when I boot the other OS. This would save me disk space as I won’t have to install the program twice.
I’m dual-booting Windows ME and Windows XP pro.