weaning

(just posted this on the breastfeeding board, but I thought I'd try here too!)

how do i wean from breast to milk in a sippy cup?? I breastfeed exclusively 5 times a day...I just don't know how to go about substituting the feedings for reg. milk. I want to wean gradually (substituting one feeding for milk every week-two weeks) but it seems like a lot for him to eventually have 5 cups of milk a day....and how much milk (how many ounces) do I put in the sippy cup? Thank you in advance for your help!