As stated elsewhere here, Last Chaos places huge demands on your computer's resources. If you are running the game and still experience large amounts of lag, check out the recommended computer resrouces for the game -- note I said recommended, not minimum.
If your computer meets the recommended resources to play the game, you should not have any major problems playing it. If your computer does not meet these, you need to upgrade your computer or strongly consider moving to a less demanding game.
Sadly, most, of not all the good games out there require fairly up-to-date equipment. The days of being able to have almost all the new games work properly using a P3 Processor, 256MG RAM and 32MG video are over.