Installing WhatsApp on Linux is a little different from Windows. In this video you will find a useful step-by-step tutorial on how to download and install Whatsapp messenger for Ubuntu Pc (desktop).
If you are looking for a different version of Whatsapp, for windows or for a specific mobile phones brand like samsung, then whatsappfor.org offer several good tutorials.
The following video instead has been created specifically to run the Android whatsapp version for Ubuntu 12.04 LTS using one of the 5 best Android emulators (based on techapple.net review). Enjoy!