Do you mean a draft between the double glazing units an the frame. The units are notmally held in by beading on one side (could be inside or out) that pops into place - check that. If the beading is external they may also be clipped or taped underneath as a security measure.
I'm confused - think the have a termiology difference.
So the fixed (non-opening) double glazing units have a draft between them and the main frame? Not quite sure what you mean by "small frame" - the fixed units normally sit straight into the main frame (held in by beading).
The frame should be screwed in to the wall and the lintel above. It sounds like the top screws are missing..
The frame should also be foamed in to stop leakage, so a good idea would be to either remove the glass and screw the frame in then foam it, or just foam it as it is. The foam will hold it in and create a good seal.
I tihnk it depends on how the window was designed. If you have 'dummy sash' windows (so creating an even sight line across the windows, opening or not) for UPVC they effectively build an opening window but without the handles etc - which is then screwed to the metal outer frame in the same way as the opening windows. If that isn't the case they should be mounted directly in the frame with clip-in beading as Stevesy says.
If on the other hand we are all just confusing each other, then a piccie would certainly help
So, as PXW suggests, it's dummy opener (presumably for asthetic reasons). Looks like it externally beaded, so you'll probably need to pop the beading out on the outside and then remove the glazing unit to access the screws/fixings that are holding the dummy opener in place.
Problem will be that there may well be security clips under the beading the that require a special tool to release (to stop low life, simply removing the glazing to get in). With a bit of time/effort you may be able to figure out how the clips work, otherwise you'll have to track down a tool (try your nearest dodgy pub).