How do I have MIRC type for me in the chat rooms

If you mean just regular typing, you still have to do that, however, what you can do, if there are things that you say a lot and/or on a regular basis, is to create an alias that will send the message to the channel with only a few keystrokes from you.
Example: If you want to greet each person that comes into the channel using the channel name and their nick, instead of typing something like "Hi Mark, welcome to #Games-R-Us" when Mark arrives
and "Hi Jo-anne, welcome to #Games-R-Us" when Jo-anne arrives, you could make an alias
You would put that into the remotes section of your mIRC client, then when someone joins the room, you type /welcome
Just make sure that you type that in the edit box for the channel.

If that doesn't resolve what you're looking for, then please reply with more specifics.

If you want it to actually type what you say, you have to use a speech to text program for that. Dragon Naturally Speaking, Vista's built-in one, etc.

Like I want to make a auto massage in the channel like every 5 minutes,saying something like "Theres a battle at 12" and in the next 5 minutes saying it again "Theres a battle at 12" ,so everybody can see it while others is talking together without me typing over and over again every 5 minutes..

That will require a timer
eg:
Note: Using this may violate channel rules, so use at your own risk, or change the 300 to match or exceed the number of seconds that the channel ops will allow automated messages (presuming that they do allow them)