I also heard that it was harder to get into UM if you go to UM undergrad, but I followed this up with some research, and it turns out that the break down is as follows: approximately 50% out of state students, 50% in state students. Of the instate students 80-90% of them are from UofM undergrad. So compared to in state students that went to other schools, you have a better chance. As for numbers, it is indeed VERY hard. I had a 35, but subpar gpa, and I didn't get an interview. I think the advice for 34+ and high GPA (3.7-3.8+) is accurate. Of my friends that got in from UM undergrad, they had 35-38's, and 3.8+ in difficult fields (CMB, Chem engineering, Micro, Chem), and they were VERY active on campus. If you don't have these numbers or activities, its still worth a try, and remember, there are plenty of great schools out there besides Michigan. Good luck.
sscooterguy