I will be starting P90X soon and was wondering if I should eat dinner before or after the workout. Which is better to get the best results?

Generally speaking you shouldn't eat any big meals within about an hour of your workout. Make sure that after the workout you replenish your body with some form of a recovery drink (even chocolate milk works).

it'll depend on what works for you, and how you feel. i had to eat dinner first, because when i got home from work, i was just too hungry to workout. so i'd eat, wait about 60-90 min, workout, and recovery drink right after. sometimes, if it was still "early" i'd have anohter small "meal" about another 60 min after the recovery drink. if not, it was just off to bed. not ideal, but its what worked for me.