As Lance mentioned, loan programs do change frequently. I just asked a lender this same question at the beginning of January, and the answer was:
It really depends on the size of the loan, whether there are any businesses in the building, who will occupy the units and where the building is located, however, typically speaking about 30% down is needed for such a purchase.
I know the "it depends" parts of the answer probably aren't very helpful, but without knowing the details of the building, it will be hard for anyone here to give you a "real" answer.
The best advice? Talk to a lender you trust. If you don't have one, I'm sure you can find a good referral from one of the many experts here on Trulia, including yours truly. :-)
All the best!