My surgery is May 3 2007

I am scheduled to have my surgery May 3 2007. I have been to see the nutrionist and the Psychologist now I'm just waiting. I have read a lot about a Pre-op diet, my Doctor hasn't mentioned this to me yet, will this be sprung on me at some point. I want to go through that phase because I feel I need it and a lot of people seem to have shed some pounds before surgery. Is it fare to say that on an average I can expect to lose around 2 lbs a week after surgery. I walk about 2 miles a day.