using comp with HDTV as monitor

I have alot of avi's on my comp, which due to lack of dvd's, I just stream to my HDTV in 1080i. Now, would I get a better picture if I first converted to dvd format and then stream it, or should I just leave it as AVI. I hear alot of people are able to get high def media from their comps, and im not sure how this pertains to movie media.