(Wasn't sure if I should put this in the Modeling section, but since it dealt with ODFs, I put it here).
Well this is going to sound like a completely n00b question but do I have to reference a lowrez model in an ODF anywhere, or just keep them in the same folder? ty

Only units (and maybe vehicles, I can't remember) have their lowres mesh called for in their ODF. Everything else has their lowres geometry stored in the normal model.

Does that mean I don't have to make lowrez models for anything else, or just that I don't have to reference it?

If you are making your own models, props and buildings for example then you create a lowres version of the model which when your model it is exported along with it so it is all in 1 msh and the game looks after where it switches from hires to lowres. Now if you don't mind your prop or building dissappearing after 15 feet then you don't need to make a lowres.

Unit model do require a separate lowres msh and set of animations. It can use the same skeleton
but reqiures it's own separate munge process. Look in the animation directory for examples.

So I create a lowrez and put it, say next to the highrez in XSI for instance?

yes
here are two tutorials searching for "lowrez" turns up: one and two

Extremely helpful, thanks all!