How to run 32bit software in 64bit Windows7?

Well  the operating system will automatically installed it on (X86) program files which is32 bit.

 

simple as you run software on32bit windows7

If your concern is about drivers, then you need to obtain the drivers meant for64-bit OS.
For other software, Windows764-bit should run it just fine with no problem.
In case you face any problems, consider WOW64.
More info on WOW64: http://msdn.microsoft.com/en-us/library/windows/desktop/aa384249(v=vs.85).aspx