1. You can install bluestacks android emulator that usually plays all the android apps on windows.
2. Another best alternative is to use Manymo...
Go to www.Manymo.com and create an account there.
Sign up for a Free account on Manymo.com and verify your account by clicking on the registration link in your email account
Download whatsapp.apk from official website-www.whatsapp.com
Click on "Launch Emulators" and select Launch by App.
On the page that follows, click on the Upload button
Now browse the whatsapp.apk you have downloaded in step (3).
Now choose you resolution and a OS
Hit the launch button for the emulation to start.