who wants to loan me money?

[Evil Robot]

OK, I got he terminolgy wrong (I haven't got my license yet, OOPS!) But one thing I do know is that no real estate agent may sell property that that agent currently owns. This is a grave conflict of interest.
You should really consider consulting a third party agent to make sure that giving your agent a down payment in the form of a monthly payment is legal. I say this since in the event you cannot aquire a mortgage, you would want to get your down payment back. But since your living in the place at the same time, this down payment would be considered rent and non refundable.
Basicaly, you are trying to buy a house in the reverse order that most poeple would go about it and your leaving yourself open to loose a lot of money if you can't get financing (I doubt that but it's always a possibility). I just don't wan't to see you loose all the money you could have spent on a different house.