First method : Use web-based tools.
There are two tools available. You just go to their site and start typing in Guajrati. It is that simple !
Second method: Setup your Windows XP comptuer to write in Gujarati.
Actually, it is very easy to your computer for writing in Gujarati. Only about 10 minutes worth of setup and you are ready to start writing in Gujarati. If you have older version of Windows than I strongly advice you to upgrade to XP for its language capabilities. So lets get started.