How can i hide the caption (or title bar) of a window? i need it to make 2D UI using just DirectX and COM and i'm stuck at hiding this bar. I searched on google but it's just for C#, VB or MFC (that i can't use).
The caption isn't present by default -- you need to specify the window style you want.
take a look at the styles you can choose from that you pass to CreateWindowEx. You want something like WM_POPUP, which creates a window with no borders or captions -- and not something like WM_OVERLAPPEDWINDOW which gives you the whole shebang.