How could I structure this deal?

[Clinton Davis]

This is my first attempt @ owner financing so sorry for the newbie question....I have someone who is willing to sell me his property via owner financing.  However, he still has a balance on his mortgage of $45k.  Going to check to see if his loan is assumable but I doubt it.  But assuming it isn't....with :

purchase price $85k

20% down (17,000)

owner finance remaining $68,000 @5% for 15yrs.

is it possible I could buy the property from him even though he has a balance of 45k? Or does this really only work if the property is free and clear of liens?  

Thanks for the help.