|As mentioned, since the days of Win9x (even Win3.x), most applications generally have to be installed to work properly; generating registry entries for various reasons. Some of they may work with little trouble, others may crash on exit or start-up. Some may not start at all. The exception to that being that if the apps are "portable" (such as those at portableapps.com).|
Also, you mention that several apps can't be "downloaded" onto Win7 (I'm assuming you mean installed to Win7). If they won't work by installing them, you won't get them to work by "shoehorning" them in by moving the drive without its' former OS.
"Channeling the spirit of jboy..."