Frames probably aren't the method of choice for fixing screen size - I would be tempted to use a single-cell table of fixed size, with the horizontal and vertical position set to center.
That said, if you want to use frames for this, you should remember that frames are nested, so create one frameset that splits the screen vertically, then inside the middle frame, put another frameset that splits the screen horizontally. Use the following attributes for flush frames with no borders:
framespacing="0"
border="0"
frameborder="0"