I made a completely new mesh with 3ds max 2011 and followed this guide http://geck.gamesas.com/index.php/Basic_Guide:_From_Modeling_Program_to_the_GECK#For_Melee_Weapons_and_Misc_Items but when it comes to looking for your NIF file in the GECK, mines not there.

Okay, i found the NIF, but it says "invalid directory"

The NIF has to be in a very specific parent directory in some cases. A creature has to be in the "data/meshes/creatures" directory for instance. It can be in a sub-directory below that, but the main directory has to be the same (though I'm not entirely sure creatures are one of the restricted ones).

don't think so about that one- while my custom does have an issue, it does work as a creature. it's directory is meshes\starwars\droids\astromech\

only things that creep into my mind for hardcoded file paths are the player/npc anim folders.

Odds are you've placed it outside of Fallout\Data.