Hi Heiner,

> if it is not possible already (and i missed it), I would like to suggest a option,
> which excludes frozen objects from beeing snapped to.

There's an option available for that under Options > Snaps > Object snap options > "Snap to locked objects", here:




> Then the qustion: Is it possible to put a image in the background of the viewport
> to use it as blueprint?

Yes, you can use the View > Image command (under the View section of the side pane) for doing that.
See here for some more description on how to use it:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2546.44

- Michael