I have free energy; good idea to mine BTC/LTC? I don't need to pay for power to my computer. Is it a good idea to mine LTC or BTC on Intel Core Duo processor?

My CPU is 2 x 2.6GHz  (computer woks 24/7)
Mining on both Bitcoin and Litecoin is now dominated by ASICs. Even with Litecoin, you'd only mine at best about US$0.45 worth in a year.

You should have better luck if you can find a cryptocoin based on something besides SHA-256 or scrypt, for which there is no GPU or ASIC mining, such as Riecoin or Darkcoin. http://cpucoinlist.com/ lists some more CPU-friendly coins.