Yes, I agree, "generally speaking, you can install a program in the same place from 2 os's, however due to the way windows works, most programs need to be installed on both os's."
And there are recommendations on how to do it correctly:
<A HREF="http://support.microsoft.com/support/kb/articles/Q236/9/05.ASP" target="_new">FF2000: How to Install Office 2000 on a Dual-Boot System</A>
But again, generally speaking, you are sort of looking for troubles by doing that.
Without going deeply into discussion on how software works, just want to say that unfortunately, some applications install different executable files for each OS, in which case you have to create separate directory structures. You can't predict which applications will install different executable files, so you need to rely on experience to learn which applications behave this way.
You might also have trouble uninstalling an application that the OSs share. The OS from which you first run the uninstall process will delete the executable files and libraries and will remove entries for the application from the OS's Registry database, but the OS won't touch the other OS's Registry. When you dual-boot to the other OS, the uninstall process might fail because the executable file is missing. Then, you need to reinstall the application before you can uninstall it.
Be aware, that <A HREF="http://support.microsoft.com/support/kb/articles/Q221/9/17.ASP" target="_new">
“…Microsoft has confirmed this to be a problem in the Microsoft products…”</A>
NOTE: Office Setup installs Microsoft Internet Explorer to the \Program Files\Internet Explorer folder of the operating system drive by default. This is the recommended installation method for Microsoft Internet Explorer.
When you make changes to options within Microsoft Office programs, those changes may not be recognized in the other version of Windows and may need to be configured while you are running the program in the other version of Windows. Especially when you run patches and updates.
With the price about $3 for 1 GB harddrive space (my 41 GB Deskstar) and with Office directory taking about 168 MB of space and ~22 MB for IE, I don't think that I would save much by dual-boot Office installation.