It is very difficult to get an analog connection looking good. DVI and HDMI resolved the tweaking needed to get the display looking right.
Anyway, there's a program called Powerstrip that you'll neeed to download. Get it here
. This program has oodles of tweaks to get your TV display looking as good as possible. Hopefully this can get you by until you get a DVI/HDMI television.
Make sure you are running at 1920x1080 @ 30Hz for your 1080i connection and then try powerstrip to fine tune everything.