how do i go about having somone talking to my char that is not in the scene at all.
do i still need a char or can i have some kind of hidden object?
AGS is made so that it always needs to have a player character in current room. But ofcourse he may be hidden.
There are several ways to achieve this, you may choose one depending on situation.
If this is a room where player character will never appear, you may set Room's property "ShowPlayerCharacter" to False.
If player character may be visible in this room some other time, but you just need to hide him for now, you may, for example, put him beyond room borders. Like setting his X coordinate to -1000.
Other method is to create a View which consists of transparent 1x1 pixel sprites and assign this view to character as his NormalView.
In the Room Properties pane, set 'ShowPlayerCharacter' to False. You might want to go back through the manual and perhaps Densming's tutorial videos (http://www.youtube.com/user/densming). They cover a lot of the basic stuff like this.
If all else fails, I find that Google yields better results than the forum's in-house search engine. Try it like this (http://www.google.com/?q=site:adventuregamestudio.co.uk+%22your+query+here%22).
EDIT: In re-reading your original (slightly unclear) question, you may actually be asking about your visible player character talking to an invisible non-player character. I'm not sure about the best practices for that scenario, but perhaps this clarification will lead someone else to supply them for you.
You can hide a character simply by setting their transparency to 100:
cSomeguy.Transparency = 100;
It can be hard to find a certain solution on the spot but it seems like you aren't using the forum search at all. Everything you have asked so far is pretty basic and has been asked and answered multiple times already.
Make sure you exhaust the available resources before opening a thread. If you keep having basic problems I suggest you put them all in one thread.