Unlike other analog sensors, DHT22 requires only a digital pin (and on OpenSprinkler all analog pins can be used as digital pins as well). Adafruit has a tutorial on it:
https://learn.adafruit.com/dht
Basically you just need VCC, GND, and any spare pin to connect to DHT22. You do have to modify the firmware to read the value from DHT22. You can also display it to the LCD.
If you prefer using other sensors, like the MCP9700 analog sensor, you can use any of the spare analog pins.