Windows 7

Enable Punjabi Support on Windows 7 is very Easy!
Control Panel
Load the control panel by clicking on the "Start"' menu and pressing the "Control Panel" icon. Make sure you are in category view. Select the icon that says "Clock, Language and Regional Options" and then select "Region and Language"

Region and Language

Select the "Format" tab and make sure you select the option saying "English (USA)" and select "Punjabi (India)".

If you are outside India, please use "Additional Settings" and Change Currency or Select "Location" Tab to select Location.

Input Languages

Select Tab "Keyboards and Languages". Press "Change keyboards" button. This should load a dialog box asking you which input language to add. Select "Punjabi" from the drop-down list.
Now select "OK". This should now enable you to both read and write Gurmukhi on your Windows 7 computer. If you want a language bar, you can select it by pressing the "Language Bar..." button on the "Text Services and Input Languages" dialog and then selecting "Show the language bar on my desktop". The language bar enables you to visually select the keyboard layout you are using.
Once this is done, press "OK" on all remaining dialog boxes. Congratulations - you should now be able to use Unicode Gurmukhi!

Type Punjabi On Desktop
Now you can see icon near Notification area with "EN" as shown

You can use the combination ALT + SHIFT to switch between different keyboard layouts (e.g. from a English Keyboard to Gurmukhi and vice-versa).

Don't know Punjabi Keyboard?
if you are new to Punjabi input and don't know Punjabi Keyboard Layout, there is easy solution to input Punjabi "On-Screen Keyboard".
On-Screen Keyboard can be accessed by clicking on the "Start" -> All Programs -> Accessories -> Ease to Access -> On-Screen Keyboard"

Please use the combination ALT + SHIFT to switch between English and Punjabi.