In the latest version of litecoin, look for these in main.cpp:
/** Fees smaller than this (in satoshi) are considered zero fee (for transaction creation) */
int64 CTransaction::nMinTxFee = 2000000;
/** Fees smaller than this (in satoshi) are considered zero fee (for relaying) */
int64 CTransaction::nMinRelayTxFee = 2000000;
int64 CTransaction::GetMinFee(unsigned int nBlockSize, bool fAllowFree,
enum GetMinFee_mode mode) const