Sanj:
The undergrad school does make somewhat of a difference, but it will never be a deciding factor of whether a person will get accepted.
And I think here is where MCAT comes in, if you go to Harvard and get a 3.5 and 20 on your MCAT you will be at disadvantage to someone who goes to a unknown school and gets a 3.5 and 36 on his/her MCATs. MCAT, like death, is a great equalizer.
Arti