I've run into a few cases in the last few weeks when building a 32-bit installer that will run on either XP or Vista and the prerequisite installer is different (XP uses a .exe, Vista a .msu file). It would be really cool if I could set conditions for the prerequisites so that the Vista version would not show item twice, once satisfied and once not (which is really confusing to the end user).
Currently prerequisites cannot be hidden based on the target OS. However, this improvement is on our TODO list and it will be available in a future version of Advanced Installer.