no, setframe requires a frame. you can use NSMakeRect(float x, float y, float w, float h) as argument. then, you set the window's view with something like this:
[myWindow setContentView:someNewView];
don't start with the window staying where it is at the beginning, that's something you can always fix later. basically, this is what happens: x and the width stay the same (if you want something similar to omniweb's preferences window), the height is given by the new view, the only thing you have to take care of is the new y.
does that help?