To install this script just load it into your alias's and type:

/awayscript

It will autmatically post a message to all channels when u sign away and every now and then. When you are ready to return just type /back

Also in the Variables section make a variable called %password and set your normal password as this will automatically remember your nick and return you to it. Also set %awaynick to something.

awayscript {
  /set %away Yes
  /set %awayreason $1-
  /amsg 1,14I am now Away: 14,15 %awayreason
  /timer 1 300 /timeraway
  /set %nick $me
  /nick %Awaynick
}
timeraway {
  if (%away != No) {
    /amsg 1,14I am Still Away
    /timer 1 300 /timeraway
  }
}
back {
  /set %away No
  /amsg 1,14I am Back From: 14,15 %awayreason
  /nick %nick
  .msg nickserv identify %password
}