Traping closing time of application(s)

My prob is to trape the closing time of an redymade application which is already installed. Actually i want to find out the duration of wark on any application in general.
How long an operator works on that application like MS Word,VB etc. So i want to trap the closing time of Word ,vb etc.That might be possible thr. either API Programming or Win Registry change.

if u know then please provide me the code or write me the logic at least

Thanks

Prabhash