correct me if i didnt understand the last part of your answer correctly;
so if install microsoft word on vista and win7 then i will have to install it twice no matter what in order to run it on both OSes?
Yes you will have to reinstall whatever app on each OS for it to work, you can't just install an app to a partition and expect it to work in each OS.. the only way that works is if the app only has an .exe file and no installation is needed.. like cpu-z for example, that app you can put on a partition and run it from any OS without having to install it...But for Office, yes you have to physically install it on each OS.. and as ickymay said, having the app on the same partition as the OS is a good way to have things setup..
I don't agree. I have a "programs" folder on my Local Disk( E: ) where are M$ office, opera, skype, winpatrol, and much more applications that works on both vista( C: ) and win 7( I: ). I don't have to reinstall them every time, they saves all data on different folders and everything works fine. I think that's because hardware are the same, only OS's are different.