Which software to password protect installed programs?

Cannot be done; you can only lock the entire computer.

downland app-locker from http://www.smart-x.com/  

Please do not push software that does not even address the question! hafiz48 wants to lock a RUNNING PROGRAM, not prevent the program from being executed.

it can be done even for running programs by just downloading this program,

direct link to download:

http://www.duriosoft.com/downloads/lt-setup.exe

(or)

from here,

http://www.duriosoft.com/products/lockthis/12.html

OK, that does look promising! But I am a little wary of software that installs itself that deeply into Windows. . .