Is there some kind of utility in the construction set, or do I need to write my own code source, like C or C++?

If you just want to create new stats/enchantments with the existing weapons, all you need is the construction set. If you want to make models of your own, you'll need either 3dsmax 3/4/5 (all obsolete and impossible to get legally) or blender (I think someone made a plugin for it?). If you haven't done any 3d modeling before, expect to spend a few months practicing before you get any results you'll want to put in-game.

Thank Peregrin, might you know where i can get the 3dsmaz tool? I'll look around but I'm sure I'll need some help.

The latest version is HERE. But the .nif export plugin won't work with it, so you'd be buying it for Oblivion. The only 3dsmax versions that work with the plugin are no longer being sold by the company. Besides getting lucky with a rare third-party sale that you can actually trust, the only way to get them is to download them illegally. For obvious reasons I'm not going to say where, but anyone with basic intelligence can figure out how to pirate software.

And 3D-Max is expensive, use Blender3D instead, its' free And a nif-importer-exporter ixist to, just google for "NIFLA".