ok first thing is first
To place the weapon on the table, select the weapon and click enter like you did. select the weapon again and call up it's property menu. now use the shift+pgup and shift+pgdn
That will allow you to raise and lower the weapon even better. the mouse scroll button will zoom in and out the arrow keys will move the weapon along the three axis, and the number keys will rotate it.
As for the table, to make it immobile, pull up it's properties scroll towards the bottom near where you adjusted the physics. There will be an option that says isimobile make sure this is set to yes.
Check out the community guide
http://forum.thegamecreators.com/?m=forum_view&t=131868&b=21
This will answer most common questions
Scroll to the bottom of this page, utilize the search function before posting your question, chances are its been asked before.
Hope this helps