Creating new objects

[Cookie Monster]

Si, is there a way to make new objects we create and place in Media/Tiles/Objects to work like walls or something you can't get past? For example, in NSGP you have tires, in SLR I made a meteor and would like it to work like those tire walls. (before you ask, it's not just for the meteor, I might use it for other things! and so may you.)

Thanks :)

Also while we're on this subject, mod subforum pls? And how do you add a new object to the game?