Hi, i am trying to find out how to place items on a planet. Like for my mod. How do i put an item in an object, say the pillar where Naga Sadow's poison blade is?

If you know the name of the placeable, then what you'll want to do is edit the placeable's .utc file with Kotor tool. Under the advanced tab you should be able to put checkmarks in 3 spots, "Has inventory" ,"Party interact" and "Usable". then at the bottom hit the inventory tab and add the items you want. Then drop the file in your override folder. One note though ,TSL especially, they liked to reuse the names of placeables all over the game so if in your override folder you may end up with the inventory all over the place.

yes, but which ones are they, and how do i place them. Also, the inventory list only shows the vanilla KOTOR items, not the ones i have

This tutorial should help http://www.lucasforums.com/showthread.php?t=134067)
As far as the item you want to use the easiest way to find it would be to find the item in an existing module,then use ktool and look under Rims-Modules-(the name of the module)_s.rim-Blueprint,placeables. You can name your new placeable whatever you wish.
To place it in game you can either script it to appear on enter http://www.lucasforums.com/showthread.php?t=134067) or edit the .git file of the module with kgff editor http://www.starwarsknights.com/tools.php) and add your placeable to the list.