Mesh Objects Problem

I am creating a spaceship from a YouTube tutorial at the moment. Everything was fine until just now when for some reason when I went to add a new cube mesh it seemed to become part of the model as soon as it was created. I have the curser at centre and new meshes appear in the model. Up to now I could just move the new mesh away from the model and start working on it. Now I can`t do this. When I move it the model moves as well. Is there a setting I might have clicked on without realising? Any help would be appreciated.

when I went to add a new cube mesh it seemed to become part of the model as soon as it was created.
Add new objects in object mode for them to be separate objects

When I move it the model moves as well. Is there a setting I might have clicked on without realising?
If they are separate objects ensure you don’t have proportional editing enabled (button on 3d view header or shortcut O)

Thanks Richard. I was adding them in Object Mode but it turns out I had Proportional Editing enabled. Good call. Problem sorted and I have learned something new as well. Never realised that happened in PE. http://i530.photobucket.com/albums/dd349/G00nster/Smiley%20Faces/sHa_thumb2.gif