What's the difference between charm and dire charm? I mean about the effect... they seem to do the same thing.

1. Dire charms lasts 10 rounds, charm lasts 5 rounds.
2. A dire charmed person will go berserk.
3. If you use charm on someone that gave you a quest, and you complete the quest, they may 'forget' that they ever even gave you the quest, causing you not to get an award.

what do you mean? After I dire charm someone I can control him normally.

You can control him, yes.
But there is the chance he will turn on you during combat.

Minsc can go berserk, but send him into combat, with you next to him, and he might attack you when your enemies are dead, too. ;)