Deepavali and Lakshmi Puja are one of the most important Hindu festivals in Tamil Nadu. Deepavali in 2012 in Tamil Nadu is on November 13. Lakshmi Puja will be held on November 13. There is also a Surya Grahan on November 13 but not visible in India - visible in Australia and New Zealand. The solar eclipse will not affect the Diwali in India.
In Tamil Nadu and generally in
South India, Deepavali is celebrated to commemorate the killing of the demon Narakasura by Lord Krishna. In Karnataka, it is observed as Bali Paadyami to mark the day of King Bali's return to his subject once a year. In Kerala, Deepavali is a low-key affair and some people consider it as the return of Lord Ram from exile.
There may be difference in date and myth but the central theme that good wins over evil, remains the same.
North India, Diwali commemorates the return of Lord Ram along with Sita and Lakshman from his 14 years of exile after killing Ravana.