How can Win+P be disabled in Windows 7?

You can disable Win-P with a simple AutoHotkey script, that consists of four characters:

#p::

1. stands for windows key

2. p is for - well - p
3. The :: is for "hotkey"

If you want to run the command prompt with Win-P the code will look like this:

#InstallKeybdHook ; to make extra sure the keys are caught by AutoHotkey 
#p::run cmd.exe

I've tested both and they work for me under Windows 7 Ultimate. If you don't want to install AutoHotkey, download the zip, create the script in an editor and save it with the .ahk ending. If need be, it can be compiled into an .exe.

I have actually created a pretty nice post about disabling hotkeys with AutoHotkey.

Using AutoHotkey, you can customize and remap pretty much any key or hotkey on your keyboard.

But essentially I agree: any decent program should come with a built-in functionality to customize or disable hotkeys for certain functions.