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
alias welcome {
.msg $chan Hi $nick $+ , welcome to $chan
}
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.