Forums Scripts & Popups Filling custom window with text using dll

How exactly is this to be done?
I want a dll to write some data (lines of text) in a custom window (plain custom window). Sofar I have managed to write something in the window itself (using the hwnd of the window), but this text dissapears at the first repaint (so the data must be stored somewhere else...but where?)
The dll is made with m$ vc++ 6

IM not entirely farmilir with them, but there is a sendMessage function that i believe can send executable commands (such as /echo or /aline) to mirc and hav eit run it.