Depends on the program... All of Philadelphia has interns start July 23rd, so orientation starts 1-2 weeks before that. Some programs start orientation July 1 (I was so-oo jealous of those people!). Its really variable - check with your program Thursday!
Depends on the program but most have you actually start working on July 1. We had to show up a couple of weeks early for orientation, ACLS, ATLS, etc. but the first actual workday was July 1st (which for me was a Sunday).