RS-485 is not compatible with RS-232 in voltage levels, so you'll need either a USB-to-RS-485 or RS-232-to-RS-485 converter.
Beyond that, it's really impossible to say if it will work or not. The protocol might not be compatible since you are typically not controlling exactly when the RS-485 driver relinquishes the bus (it's usually done by some kind of timer in the unit).
You might have to add some kind of delays at one end or the other to allow that to happen properly. Usually it will work out of the box, but there is no guarantee that just because the voltage levels and baud rates are compatible that the protocol will be compatible.
With RS-485 data going both ways is transmitted on a single differential pair, so the possibility of collisions exists even with only two devices on the bus.
Here is a white paper that covers the issues.