There is an article here which may answer some of those questions for you :
Windows 7: 64 bit vs 32 bit?
Basically speaking, you can run almost all 32 bit software on Windows 7 64-bit without any noticeable difference. The main problem is when you try to use 32 bit drivers or software that needs to interface/wrap with x64 compiled software.
I don't think you will have any issue running 32 bit apps in Windows 7 x64, but there are a handful of exceptions. Most things should run fine
You can run the Windows 7 Upgrade Adviser if you are thinking about upgrading a current system :
http://www.microsoft.com/downloads/d...displaylang=en
Alternatively, if you have a specific app that you are worried about, let us know and someone here may be able to shed some light on it.