Arduino with Roomba

So I got another Arduino today, and I'm trying to interface it with my Roomba Dirt Dog. It's pretty easy to do, you just send the roomba commands through the serial port and it does whatever. But I'm running into a bit of a problem. Whenever I ask the roomba for its sensor values, it just becomes unresponsive and keeps doing the last command I sent it. I even tried using the code that from Tod Kurt at His code just ends up making the roomba drive forward without responding like it should. Its like as soon as the roomba gets the sensor opcode it just goes nuts. Anybody here have any experience with this?

Edit: I forgot to mention that when I use my roomba to pc serial cable, I can read the sensor values. So it must be something in the Arduino code making it freeze.