I am replacing my old Honeywell dial t-stat with a programmable honeywell RTH230B. When I removed the old t-stat, there were only two wires, unlabeled of course. The white one was at the 6 o'clock position and the black one was at about the 8 o'clock position. After doing some research, I guessed the white wire goes to the W port on the new t-stat, and the black goes to the Rh port (this is only for heating). Am I correct in this assumption?
Also, the wires coming out of the wall don't seem to stay in the ports after I screw them down. Has anyone else had this problem? It almost seems like they are too thick to go into the small ports. I was thinking of buying some thinner copper wire to wrap around the ends in the hopes of getting a better contact in the port. Thoughts?

Yes, use the Rh and W terminals. Make sure there is no wire between Rh and Rc terminals or the furnace will come on in the summer when the thermostat tries to cool the house.

It doesn't matter which of the old wires you connect to the Rh and W terminals. It will work either way, but I suppose if you connect white to white then it may make things easier when you replace the furnace at some future time.

I have not seen this particular thermostat, but usually the ports are big enough to accommodate all typical wire sizes. If it is the kind there you put the wire in the port and then tighten the screw, then ensure the screws are entirely loosened (not off) first. When you tighten, you should be able to see the clamp move in the port as you turn the screw. If the wire is on the wrong side of the clamp, then loosen the screw, move the wire to the other side of the clamp and try again.