NifSkope is really the only way to play around with the meshes that the game uses.
If you're serious about wanting to add or modify the objects in Oblivion; not just placing ones that already exist, you're going to have to get proficient at using it. I suggest http://cs.elderscrolls.com/constwiki/index.php/NifSkope_Comprehensive_Guide comprehensive guide to NifSkope if you want to do this. It helped me out when I was learning to use it, and it's still good reference material for when I get rusty on something! I strongly reccomend using it.
Good luck!