Win2000:

To type using Microsoft's IME

Go to "Control Panel" and click on "Regional Options" 
Click "General" tab and from Language Settings for System window check on "Indic" 
It will ask for Win2000 CD. Installation will happen. Reboot the system 
Now again go to Regional Option and click on "Input Locales" tab 
Add the languages in which you want to type. 
A small "EN" will appear in the system tray. Left click on "EN" and choose the language to type. 

Win XP:

To type using Microsoft's IME

Go to "Control Panel" and then click "Regional and Language Options" 
Click on "Languages" tab and check on the box which says "Install Files for complex scripts". 
This method will ask for Win XP CD. Put the CD in the CD drive and let the installation begin. 
Once the installation is complete boot the system if required and again goto 2nd step. 
Now click "Details" tab. Click on "Add" to add the languages of your choice. 
A small "EN" will appear in the system tray. Left click on "EN" and choose the language to type