My old thermostat was janitrol HPT 18-60 and wires were:
Y (yellow)
G (orange)
R (Red)
O (orange)
W2 (white)
E (Black)
C (Blue)

I just bought a Honeywell #RTH6300B. Their wires are: G,W,Y, R,RC. How can I match them up? Do I need the "O" on the old one? We are only getting hot air now by matching Y-Y, G-G, R-R, W2-W, orange, brown, and blue are not connected at this time... Any help would be GREATLY appreciated!

Sorry for the delay, just noticed your post. Even thou you probably all set by now I will still offer that you appear to have a heat pump system, judging by the O, which usually is for a reversing valve, W2 which usually is for the auxiliary heat when the ambient air does not contain enough latent heat available, and E, which I do not know at this time.

The new stat you have is only for a standard heating/cooling system and will not control your system, as the other wire will need to be used.

Again, sorry for not seeing your post in time. Hope this helps.