如何基于每个系统主题定义图标资源？

I have a WPF 4.0 application that utilizes some custom 16x16 icons in things like menu commands and the like. I'd like to have (for now) two sets of icons, the default Vista/7-ish ones and some XP-ish ones. What I want is to have the current OS determine which icons to use.I have a WPF 4.0 application that utilizes some