I don't see any reason to wait to start weights. I go to the gym 4 days a week, each day I do 1/2 hour of cardio (switching around on the machines to keep from getting "settled" into a routine), then 2 days I concentrate on upper body weights and 2 days lower body.
My main advice is that you can do just about as much cardio as you want, but make sure that you give each muscle group you lift at least 1 full day of rest before lifting again. I go upper, lower, rest, upper, lower, rest, rest.
Good luck. I love my time at the gym (well, 95% of the time
), I hope you enjoy it as well!