Kunjuppu ji,
I think Kerala temples practice discriminating other religious people from entering Hindu temples. Probably Sabarimala is the only exception but here also ladies of a particular age group are discriminated.
In Tamilnadu, there is no discrimination of people entering temples. Certain temples have the board, `only Hindus permitted beyond this limit'. But here also foreigners if they prove that they have converted to Hinduism, they are permitted. One of our own member `Easternmind' narrated his experience at Madurai Meenakshi temple which is available in our forum threads.
To the best of my knowledge, KC Abraham, Ex Governor of Andhra Pradesh was admitted to Tirumala temple at Andhra Pradesh after he expressed his faith in the Hindu God. Sonia Gandhi has visited Tirumala temple inspite of her Christian origin.
All the best