To build a mockup or demonstration page of your layout, the method you describe should work OK. To build a real web page, it will fail miserably.
Now, tell us - you are creating a slice that is (say) 300x200px, and when you export from PS, this image exports at 1024x768? And by the way, there is no need to do the image of the browser thing. Just make your photoshop canvas be the right size and design to the edges of the canvas. By the way #2, 1024 is a bit wide. To fit comfortably in a 1024 screen, your maximum width should be about 960-980px.