The old thermostat had:

X2
O
G
Y
T
R
W
B
It also had U and F, but they were not used.

So far I have wired the Honeywell RTH2300 as follows:
B to B
O to O
G to G
Y to Y
W to W
R to R

I have a T (tan) that I have capped off and a X2 (black) that I do not have hooked up. I believe the X2 is for the Emergency Heat.
I do not have any heat/AC/or fan working.

Any ideas?