say I know a file name how to I save that file to the hd?

[smoth]

Like say I want to write some custom code to export an image out of gundam into a file via lua? like say a model, how would I do this?

[Argh]

For writing image data, use gl.SaveImage.

In terms of details, a good method is to render the Unit to a FBO, then save the results. See jK's unit-icon creation script for an example.