Assigning meshes & materials from Assets, how?

I know this must be plainly simple, but still it eludes me:

I want to create a mesh and/or material (in an Editor script), and I want to assign a mesh from my assets. Not necessarily in Resources folder mind you, just some random asset.

something like:

gameObject.GetComponent(MeshFilter).sharedMesh = ?LoadAsset? ("big_gun_mesh");

Is this possible?

You'll want to use AssetDatabase.LoadAssetAtPath:

http://unity3d.com/support/documentation/ScriptReference/AssetDatabase.LoadAssetAtPath.html

It's similar to Resource.Load, but takes paths relative to the project folder, not assets as you may first guess