Now dealerships are installing CNG in XLi/GLi 2009 onwards. Previously they said that you could not claim warranty if you install CNG in it. I don't know the reason behind this contradiction.
According to my information, Toyota Walton Motors (Lahore) is installing the Lambda Kit from Lendi Renzo in new XLi/GLi. The approximate price they told me was around 70 thousand. I don't have any information about this CNG kit but according to their sales representative, there is negligible different between performance on petrol and CNG with this Kit.
Rest the members using CNG in their cars can tell. I am running it on petrol till now.